WO2021060844A1 - Procédé et dispositif de codage/décodage d'image utilisant un mode palette, et procédé de transmission de train de bits - Google Patents

Procédé et dispositif de codage/décodage d'image utilisant un mode palette, et procédé de transmission de train de bits Download PDF

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WO2021060844A1
WO2021060844A1 PCT/KR2020/012898 KR2020012898W WO2021060844A1 WO 2021060844 A1 WO2021060844 A1 WO 2021060844A1 KR 2020012898 W KR2020012898 W KR 2020012898W WO 2021060844 A1 WO2021060844 A1 WO 2021060844A1
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Prior art keywords
palette
current block
mode
block
current
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PCT/KR2020/012898
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English (en)
Korean (ko)
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장형문
유선미
남정학
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엘지전자 주식회사
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Priority to KR1020227008747A priority Critical patent/KR20220047834A/ko
Priority to JP2022518236A priority patent/JP7362910B2/ja
Priority to CN202080066527.8A priority patent/CN114521328A/zh
Priority to CA3155112A priority patent/CA3155112A1/fr
Publication of WO2021060844A1 publication Critical patent/WO2021060844A1/fr
Priority to US17/697,474 priority patent/US11689732B2/en
Priority to US18/198,170 priority patent/US12003740B2/en
Priority to JP2023172537A priority patent/JP2023171923A/ja

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    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/157—Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
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    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
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    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
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    • H04N19/184—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being bits, e.g. of the compressed video stream
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    • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
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    • H04N19/96—Tree coding, e.g. quad-tree coding

Definitions

  • the present disclosure relates to an image encoding/decoding method, an apparatus, and a method of transmitting a bitstream using a palette mode, and more particularly, an image encoding/decoding method for selectively updating a palette predictor based on a split structure of a current block.
  • An object of the present disclosure is to provide a video encoding/decoding method and apparatus with improved encoding/decoding efficiency.
  • an object of the present disclosure is to provide a method and apparatus for encoding/decoding an image using a palette mode.
  • an object of the present disclosure is to provide an image encoding/decoding method and apparatus for selectively updating a palette predictor based on a split structure of a current block.
  • an object of the present disclosure is to provide an image encoding/decoding method and apparatus for selectively applying a palette mode based on a divided structure of a current block.
  • an object of the present disclosure is to provide a method for transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure.
  • an object of the present disclosure is to provide a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure.
  • an object of the present disclosure is to provide a recording medium storing a bitstream that is received and decoded by an image decoding apparatus according to the present disclosure and used for restoring an image.
  • a palette mode when a palette mode is applied to a current block, obtaining palette information and palette index prediction information for the current block from a bitstream, based on the palette information, the Constructing a palette predictor and a palette table for a current block, generating a palette index map for the current block based on the palette index prediction information, and based on the palette table and the palette index map, Decoding the current block, and the palette predictor may be selectively updated based on a partition structure of the current block.
  • An image decoding apparatus includes a memory and at least one processor, wherein when a palette mode is applied to a current block, the at least one processor includes palette information for the current block from a bitstream and Acquires palette index prediction information, configures a palette predictor and a palette table for the current block based on the palette information, and generates a palette index map for the current block based on the palette index prediction information , Based on the palette table and the palette index map, the current block is decoded, and the palette predictor may be selectively updated based on the partition structure of the current block.
  • a palette mode when a palette mode is applied to a current block, configuring a palette predictor and a palette table for the current block, based on the palette table, in the current block Generating a palette index map for, and encoding the current block based on the palette index map, wherein the palette predictor may be selectively updated based on a partition structure of the current block.
  • a transmission method may transmit a bitstream generated by the image encoding apparatus or image encoding method of the present disclosure.
  • a computer-readable recording medium may store a bitstream generated by the image encoding method or image encoding apparatus of the present disclosure.
  • an image encoding/decoding method and apparatus with improved encoding/decoding efficiency may be provided.
  • a method and apparatus for encoding/decoding an image based on an improved palette mode may be provided.
  • an image encoding/decoding method and apparatus for selectively applying a palette mode based on a divided structure of a current block may be provided.
  • a method for transmitting a bitstream generated by an image encoding method or an apparatus according to the present disclosure may be provided.
  • a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure may be provided.
  • a recording medium may be provided that stores a bitstream that is received and decoded by the image decoding apparatus according to the present disclosure and used for image restoration.
  • FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.
  • FIG. 2 is a diagram schematically illustrating an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
  • FIG. 3 is a diagram schematically illustrating an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
  • FIG. 4 is a diagram illustrating an image segmentation structure according to an exemplary embodiment.
  • FIG. 5 is a diagram illustrating an embodiment of a partition type of a block according to a multi-type tree structure.
  • FIG. 6 is a diagram illustrating a signaling mechanism of block division information in a quadtree with nested multi-type tree structure according to the present disclosure.
  • FIG. 7 is a diagram illustrating an embodiment in which a CTU is divided into multiple CUs.
  • FIG. 8 is a diagram illustrating an embodiment of a redundant division pattern.
  • FIG. 9 is a diagram illustrating an example of a luma block and a chroma block in a 4:2:0 color format.
  • 10A to 10C are diagrams illustrating an example of syntax for converting a single tree structure to a dual tree structure.
  • FIG. 11 is a flowchart illustrating a video/video encoding method based on intra prediction.
  • FIG. 12 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • FIG. 13 is a flowchart illustrating a video/video decoding method based on intra prediction.
  • FIG. 14 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • 15 is a diagram illustrating an example of a scanning method that can be used in a palette mode.
  • 16 is a diagram illustrating an example of a process of encoding a palette of a current block.
  • 17 is a diagram illustrating a part of a coding_unit syntax for a palette mode.
  • 18A to 18E are diagrams illustrating palette_coding syntax for a palette mode.
  • 19 is a diagram illustrating an example of a CTU having a local dual tree structure.
  • FIG. 20 is a diagram illustrating an example of a decoding process for respective CUs in the example of FIG. 19.
  • 21 and 22 are diagrams for explaining problems that occur when a palette mode is applied in the decoding process of FIG. 20.
  • FIG. 23 is a flowchart illustrating a palette encoding method according to an embodiment of the present disclosure.
  • FIG. 24 is a diagram for describing a palette encoding process when a palette predictor is not updated in the example of FIG. 19.
  • 25 is a diagram illustrating an example of a process of selectively updating a palette predictor based on a partition structure of a current block.
  • 26 is a flowchart illustrating a method of decoding a palette according to an embodiment of the present disclosure.
  • FIG. 27 is a flowchart illustrating a palette encoding method according to an embodiment of the present disclosure.
  • FIG. 28 is a diagram illustrating a specific example of a coding_unit syntax including a palette mode flag.
  • 29 is a flowchart illustrating a method of decoding a palette according to an embodiment of the present disclosure.
  • FIG. 30 is a diagram illustrating a content streaming system to which an embodiment according to the present disclosure can be applied.
  • a component when a component is said to be “connected”, “coupled” or “connected” with another component, it is not only a direct connection relationship, but also an indirect connection relationship in which another component exists in the middle. It can also include.
  • a certain component when a certain component “includes” or “have” another component, it means that other components may be further included rather than excluding other components unless otherwise stated. .
  • first and second are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise noted. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment is referred to as a first component in another embodiment. It can also be called.
  • components that are distinguished from each other are intended to clearly describe each feature, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated into one hardware or software unit, or one component may be distributed to form a plurality of hardware or software units. Therefore, even if not stated otherwise, such integrated or distributed embodiments are also included in the scope of the present disclosure.
  • components described in various embodiments do not necessarily mean essential components, and some may be optional components. Accordingly, an embodiment consisting of a subset of components described in an embodiment is also included in the scope of the present disclosure. In addition, embodiments including other elements in addition to the elements described in the various embodiments are included in the scope of the present disclosure.
  • the present disclosure relates to encoding and decoding of an image, and terms used in the present disclosure may have a common meaning commonly used in the technical field to which the present disclosure belongs unless newly defined in the present disclosure.
  • a “picture” generally refers to a unit representing one image in a specific time period
  • a slice/tile is a coding unit constituting a part of a picture
  • one picture is one It may be composed of more than one slice/tile.
  • a slice/tile may include one or more coding tree units (CTU).
  • pixel or “pel” may mean a minimum unit constituting one picture (or image).
  • sample may be used as a term corresponding to a pixel.
  • a sample may generally represent a pixel or a value of a pixel, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.
  • unit may represent a basic unit of image processing.
  • the unit may include at least one of a specific area of a picture and information related to the corresponding area.
  • the unit may be used interchangeably with terms such as “sample array”, “block”, or “area” depending on the case.
  • the MxN block may include samples (or sample arrays) consisting of M columns and N rows, or a set (or array) of transform coefficients.
  • current block may mean one of “current coding block”, “current coding unit”, “coding object block”, “decoding object block”, or “processing object block”.
  • current block may mean “current prediction block” or “prediction target block”.
  • transformation inverse transformation
  • quantization inverse quantization
  • current block may mean “current transform block” or “transform target block”.
  • filtering is performed, “current block” may mean “block to be filtered”.
  • current block may mean a block including both a luma component block and a chroma component block or "a luma block of the current block” unless explicitly stated as a chroma block.
  • the luma component block of the current block may be explicitly expressed by including an explicit description of a luma component block, such as “luma block” or "current luma block”.
  • the chroma component block of the current block may be explicitly expressed by including an explicit description of a chroma component block such as a "chroma block” or a "current chroma block”.
  • FIG. 1 shows a video coding system according to this disclosure.
  • a video coding system may include an encoding device 10 and a decoding device 20.
  • the encoding device 10 may transmit the encoded video and/or image information or data in a file or streaming format to the decoding device 20 through a digital storage medium or a network.
  • the encoding apparatus 10 may include a video source generation unit 11, an encoding unit 12, and a transmission unit 13.
  • the decoding apparatus 20 may include a receiving unit 21, a decoding unit 22, and a rendering unit 23.
  • the encoder 12 may be referred to as a video/image encoder, and the decoder 22 may be referred to as a video/image decoder.
  • the transmission unit 13 may be included in the encoding unit 12.
  • the receiving unit 21 may be included in the decoding unit 22.
  • the rendering unit 23 may include a display unit, and the display unit may be configured as a separate device or an external component.
  • the video source generator 11 may acquire a video/image through a process of capturing, synthesizing, or generating a video/image.
  • the video source generator 11 may include a video/image capturing device and/or a video/image generating device.
  • the video/image capture device may include, for example, one or more cameras, a video/image archive including previously captured video/images, and the like.
  • the video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate a video/image.
  • a virtual video/image may be generated through a computer or the like, and in this case, a video/image capturing process may be substituted as a process of generating related data.
  • the encoder 12 may encode an input video/image.
  • the encoder 12 may perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency.
  • the encoder 12 may output encoded data (coded video/image information) in the form of a bitstream.
  • the transmission unit 13 may transmit the encoded video/image information or data output in the form of a bitstream to the reception unit 21 of the decoding apparatus 20 through a digital storage medium or a network in a file or streaming form.
  • Digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.
  • the transmission unit 13 may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast/communication network.
  • the receiving unit 21 may extract/receive the bitstream from the storage medium or network and transmit it to the decoding unit 22.
  • the decoder 22 may decode the video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoder 12.
  • the rendering unit 23 may render the decoded video/image.
  • the rendered video/image may be displayed through the display unit.
  • FIG. 2 is a diagram schematically illustrating an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
  • the image encoding apparatus 100 includes an image segmentation unit 110, a subtraction unit 115, a transformation unit 120, a quantization unit 130, an inverse quantization unit 140, and an inverse transformation unit ( 150), an addition unit 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190.
  • the inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a “prediction unit”.
  • the transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit.
  • the residual processing unit may further include a subtraction unit 115.
  • All or at least some of the plurality of constituent units constituting the image encoding apparatus 100 may be implemented as one hardware component (eg, an encoder or a processor) according to embodiments.
  • the memory 170 may include a decoded picture buffer (DPB), and may be implemented by a digital storage medium.
  • DPB decoded picture buffer
  • the image segmentation unit 110 may divide an input image (or picture, frame) input to the image encoding apparatus 100 into one or more processing units.
  • the processing unit may be referred to as a coding unit (CU).
  • the coding unit is a coding tree unit (CTU) or a largest coding unit (LCU) recursively according to a QT/BT/TT (Quad-tree/binary-tree/ternary-tree) structure ( It can be obtained by dividing recursively.
  • one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and/or a ternary tree structure.
  • a quad tree structure may be applied first, and a binary tree structure and/or a ternary tree structure may be applied later.
  • the coding procedure according to the present disclosure may be performed based on the final coding unit that is no longer divided.
  • the largest coding unit may be directly used as the final coding unit, or a coding unit of a lower depth obtained by dividing the largest coding unit may be used as the final cornet unit.
  • the coding procedure may include a procedure such as prediction, transformation, and/or restoration, which will be described later.
  • the processing unit of the coding procedure may be a prediction unit (PU) or a transform unit (TU).
  • the prediction unit and the transform unit may be divided or partitioned from the final coding unit, respectively.
  • the prediction unit may be a unit of sample prediction
  • the transform unit may be a unit for inducing a transform coefficient and/or a unit for inducing a residual signal from the transform coefficient.
  • the prediction unit (inter prediction unit 180 or intra prediction unit 185) performs prediction on a block to be processed (current block), and generates a predicted block including prediction samples for the current block. Can be generated.
  • the prediction unit may determine whether intra prediction or inter prediction is applied in units of a current block or CU.
  • the prediction unit may generate various information on prediction of the current block and transmit it to the entropy encoding unit 190.
  • the information on prediction may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
  • the intra prediction unit 185 may predict the current block by referring to samples in the current picture.
  • the referenced samples may be located in a neighborhood of the current block or may be located away from each other according to an intra prediction mode and/or an intra prediction technique.
  • the intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes.
  • the non-directional mode may include, for example, a DC mode and a planar mode (Planar mode).
  • the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes, depending on the degree of detail of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting.
  • the intra prediction unit 185 may determine a prediction mode applied to the current block by using the prediction mode applied to the neighboring block.
  • the inter prediction unit 180 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture.
  • motion information may be predicted in units of blocks, subblocks, or samples based on correlation between motion information between neighboring blocks and the current block.
  • the motion information may include a motion vector and a reference picture index.
  • the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
  • the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture.
  • the reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different from each other.
  • the temporal neighboring block may be referred to by a name such as a collocated reference block and a collocated CU (colCU).
  • a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic).
  • the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive a motion vector and/or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes.
  • the inter prediction unit 180 may use motion information of a neighboring block as motion information of a current block.
  • a residual signal may not be transmitted.
  • MVP motion vector prediction
  • a motion vector of a neighboring block is used as a motion vector predictor, and an indicator for a motion vector difference and a motion vector predictor ( indicator) to signal the motion vector of the current block.
  • the motion vector difference may mean a difference between a motion vector of a current block and a motion vector predictor.
  • the prediction unit may generate a prediction signal based on various prediction methods and/or prediction techniques to be described later.
  • the prediction unit may apply intra prediction or inter prediction for prediction of the current block, and may simultaneously apply intra prediction and inter prediction.
  • a prediction method in which intra prediction and inter prediction are applied simultaneously for prediction of the current block may be referred to as combined inter and intra prediction (CIIP).
  • the prediction unit may perform intra block copy (IBC) for prediction of the current block.
  • the intra block copy may be used for content image/movie coding such as games, such as, for example, screen content coding (SCC).
  • IBC is a method of predicting a current block by using a reference block in a current picture at a distance from the current block by a predetermined distance.
  • the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to the predetermined distance.
  • IBC basically performs prediction in the current picture, but in that it derives a reference block in the current picture, it may be performed similarly to inter prediction. That is, the IBC may use at least one of the inter prediction techniques described in this disclosure.
  • the prediction signal generated through the prediction unit may be used to generate a reconstructed signal or may be used to generate a residual signal.
  • the subtraction unit 115 subtracts the prediction signal (predicted block, prediction sample array) output from the prediction unit from the input image signal (original block, original sample array), and subtracts a residual signal (remaining block, residual sample array). ) Can be created.
  • the generated residual signal may be transmitted to the converter 120.
  • the transform unit 120 may generate transform coefficients by applying a transform technique to the residual signal.
  • the transformation technique uses at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform).
  • DCT Discrete Cosine Transform
  • DST Discrete Sine Transform
  • KLT Kerhunen-Loeve Transform
  • GBT Graph-Based Transform
  • CNT Conditionally Non-linear Transform
  • GBT refers to the transformation obtained from this graph when the relationship information between pixels is expressed in a graph.
  • CNT refers to a transformation obtained based on generating a prediction signal using all previously reconstructed pixels.
  • the conversion process may be applied to a block of pixels having the same size of a square, or may be applied to a block of a variable size other than a square.
  • the quantization unit 130 may quantize the transform coefficients and transmit the quantization to the entropy encoding unit 190.
  • the entropy encoding unit 190 may encode a quantized signal (information on quantized transform coefficients) and output it as a bitstream. Information about the quantized transform coefficients may be called residual information.
  • the quantization unit 130 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and the quantized transform coefficients in the form of the one-dimensional vector It is also possible to generate information about transform coefficients.
  • the entropy encoding unit 190 may perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like.
  • the entropy encoding unit 190 may encode information necessary for video/image restoration (eg, values of syntax elements) together or separately, in addition to the quantized transform coefficients.
  • the encoded information (eg, encoded video/video information) may be transmitted or stored in a bitstream form in units of network abstraction layer (NAL) units.
  • the video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
  • the video/video information may further include general constraint information.
  • the signaling information, transmitted information, and/or syntax elements mentioned in the present disclosure may be encoded through the above-described encoding procedure and included in the bitstream.
  • the bitstream may be transmitted through a network or may be stored in a digital storage medium.
  • the network may include a broadcasting network and/or a communication network
  • the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.
  • a transmission unit (not shown) for transmitting the signal output from the entropy encoding unit 190 and/or a storage unit (not shown) for storing may be provided as an internal/external element of the image encoding apparatus 100, or transmission The unit may be provided as a component of the entropy encoding unit 190.
  • the quantized transform coefficients output from the quantization unit 130 may be used to generate a residual signal.
  • a residual signal residual block or residual samples
  • inverse quantization and inverse transform residual transforms
  • the addition unit 155 adds the reconstructed residual signal to the prediction signal output from the inter prediction unit 180 or the intra prediction unit 185 to obtain a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array). Can be generated.
  • a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array).
  • the predicted block may be used as a reconstructed block.
  • the addition unit 155 may be referred to as a restoration unit or a restoration block generation unit.
  • the generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, and may be used for inter prediction of the next picture through filtering as described later.
  • the filtering unit 160 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 160 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 170, specifically, the DPB of the memory 170. Can be saved on.
  • the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
  • the filtering unit 160 may generate various information about filtering and transmit it to the entropy encoding unit 190 as described later in the description of each filtering method. Information about filtering may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
  • the modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180.
  • the image encoding apparatus 100 may avoid prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus, and may improve encoding efficiency.
  • the DPB in the memory 170 may store a reconstructed picture modified to be used as a reference picture in the inter prediction unit 180.
  • the memory 170 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of blocks in a picture that have already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 180 in order to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 185.
  • FIG. 3 is a schematic diagram of an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
  • the image decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, and a memory 250. ), an inter prediction unit 260 and an intra prediction unit 265.
  • the inter prediction unit 260 and the intra prediction unit 265 may be collectively referred to as a “prediction unit”.
  • the inverse quantization unit 220 and the inverse transform unit 230 may be included in the residual processing unit.
  • All or at least some of the plurality of constituent units constituting the image decoding apparatus 200 may be implemented as one hardware component (eg, a decoder or a processor) according to embodiments.
  • the memory 170 may include a DPB, and may be implemented by a digital storage medium.
  • the image decoding apparatus 200 receiving a bitstream including video/image information may reconstruct an image by performing a process corresponding to the process performed by the image encoding apparatus 100 of FIG. 2.
  • the image decoding apparatus 200 may perform decoding using a processing unit applied by the image encoding apparatus.
  • the processing unit of decoding may be, for example, a coding unit.
  • the coding unit may be a coding tree unit or may be obtained by dividing the largest coding unit.
  • the reconstructed image signal decoded and output through the image decoding apparatus 200 may be reproduced through a reproducing apparatus (not shown).
  • the image decoding apparatus 200 may receive a signal output from the image encoding apparatus of FIG. 2 in the form of a bitstream.
  • the received signal may be decoded through the entropy decoding unit 210.
  • the entropy decoding unit 210 may parse the bitstream to derive information (eg, video/video information) necessary for image restoration (or picture restoration).
  • the video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
  • the video/video information may further include general constraint information.
  • the image decoding apparatus may additionally use information on the parameter set and/or the general restriction information to decode an image.
  • the signaling information, received information, and/or syntax elements mentioned in the present disclosure may be obtained from the bitstream by decoding through the decoding procedure.
  • the entropy decoding unit 210 decodes information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and quantizes a value of a syntax element required for image restoration and a transform coefficient related to a residual. You can print out the values.
  • the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and includes information on the syntax element to be decoded, decoding information of the neighboring block and the block to be decoded, or information of the symbol/bin decoded in the previous step.
  • the context model is determined by using and, according to the determined context model, the probability of occurrence of bins is predicted to perform arithmetic decoding of the bins to generate a symbol corresponding to the value of each syntax element.
  • the CABAC entropy decoding method may update the context model using information of the decoded symbol/bin for the context model of the next symbol/bin after the context model is determined.
  • information about prediction is provided to the prediction unit (inter prediction unit 260 and intra prediction unit 265), and the register on which entropy decoding is performed by the entropy decoding unit 210
  • the dual value that is, quantized transform coefficients and related parameter information may be input to the inverse quantization unit 220.
  • information about filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240.
  • a receiving unit for receiving a signal output from the image encoding device may be additionally provided as an inner/outer element of the image decoding device 200, or the receiving unit is provided as a component of the entropy decoding unit 210 It could be.
  • the video decoding apparatus may include an information decoder (video/video/picture information decoder) and/or a sample decoder (video/video/picture sample decoder).
  • the information decoder may include an entropy decoding unit 210, and the sample decoder includes an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, a memory 250, It may include at least one of the inter prediction unit 260 and the intra prediction unit 265.
  • the inverse quantization unit 220 may inverse quantize the quantized transform coefficients and output transform coefficients.
  • the inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block shape. In this case, the rearrangement may be performed based on a coefficient scan order performed by the image encoding apparatus.
  • the inverse quantization unit 220 may perform inverse quantization on quantized transform coefficients using a quantization parameter (eg, quantization step size information) and obtain transform coefficients.
  • a quantization parameter eg, quantization step size information
  • the inverse transform unit 230 may inverse transform the transform coefficients to obtain a residual signal (residual block, residual sample array).
  • the prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block.
  • the prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on the prediction information output from the entropy decoding unit 210, and determine a specific intra/inter prediction mode (prediction technique). I can.
  • the prediction unit can generate the prediction signal based on various prediction methods (techniques) described later.
  • the intra prediction unit 265 may predict the current block by referring to samples in the current picture.
  • the description of the intra prediction unit 185 may be equally applied to the intra prediction unit 265.
  • the inter prediction unit 260 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture.
  • motion information may be predicted in units of blocks, subblocks, or samples based on correlation between motion information between neighboring blocks and the current block.
  • the motion information may include a motion vector and a reference picture index.
  • the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
  • the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture.
  • the inter prediction unit 260 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or a reference picture index of the current block based on the received candidate selection information.
  • Inter prediction may be performed based on various prediction modes (techniques), and the information on prediction may include information indicating a mode (technique) of inter prediction for the current block.
  • the addition unit 235 is reconstructed by adding the obtained residual signal to the prediction signal (predicted block, prediction sample array) output from the prediction unit (including the inter prediction unit 260 and/or the intra prediction unit 265).
  • a signal (restored picture, reconstructed block, reconstructed sample array) can be generated.
  • the predicted block may be used as a reconstructed block.
  • the description of the addition unit 155 may be equally applied to the addition unit 235.
  • the addition unit 235 may be referred to as a restoration unit or a restoration block generation unit.
  • the generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, and may be used for inter prediction of the next picture through filtering as described later.
  • the filtering unit 240 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 240 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 250, specifically, the DPB of the memory 250. Can be saved on.
  • the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
  • the reconstructed picture (modified) stored in the DPB of the memory 250 may be used as a reference picture in the inter prediction unit 260.
  • the memory 250 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of blocks in a picture that have already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 250 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 265.
  • embodiments described in the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the image encoding apparatus 100 are respectively the filtering unit 240 of the image decoding apparatus 200, The same or corresponding to the inter prediction unit 260 and the intra prediction unit 265 may be applied.
  • the video/image coding method according to the present disclosure may be performed based on the following image segmentation structure. Specifically, procedures such as prediction, residual processing ((inverse) transformation, (inverse) quantization, etc.), syntax element coding, filtering, etc., which will be described later, are CTU, CU (and/or TU, PU) can be performed.
  • the image may be divided in block units, and the block division procedure may be performed by the image dividing unit 110 of the above-described encoding apparatus.
  • Split-related information may be encoded by the entropy encoding unit 190 and transmitted to a decoding apparatus in the form of a bitstream.
  • the entropy decoding unit 210 of the decoding apparatus derives a block division structure of the current picture based on the division-related information obtained from the bitstream, and based on this, a series of procedures for decoding an image (ex. prediction, residual). Processing, block/picture restoration, in-loop filtering, etc.) can be performed.
  • Pictures can be divided into a sequence of coding tree units (CTUs). 4 shows an example in which a picture is divided into CTUs.
  • the CTU may correspond to a coding tree block (CTB).
  • CTB coding tree block
  • the CTU may include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples.
  • the CTU may include an NxN block of luma samples and two corresponding blocks of chroma samples.
  • the coding unit is obtained by recursively dividing a coding tree unit (CTU) or a maximum coding unit (LCU) according to a QT/BT/TT (Quad-tree/binary-tree/ternary-tree) structure.
  • CTU coding tree unit
  • LCU maximum coding unit
  • QT/BT/TT Quad-tree/binary-tree/ternary-tree
  • the CTU may be first divided into a quadtree structure. Thereafter, leaf nodes of a quadtree structure may be further divided by a multitype tree structure.
  • the division according to the quadtree means division in which the current CU (or CTU) is divided into four. By partitioning according to the quadtree, the current CU can be divided into four CUs having the same width and the same height.
  • the current CU corresponds to a leaf node of the quadtree structure.
  • the CU corresponding to the leaf node of the quadtree structure is no longer divided and may be used as the above-described final coding unit.
  • a CU corresponding to a leaf node of a quadtree structure may be further divided by a multitype tree structure.
  • the division according to the multi-type tree structure may include two divisions according to the binary tree structure and two divisions according to the ternary tree structure.
  • the two divisions according to the binary tree structure may include vertical binary splitting (SPLIT_BT_VER) and horizontal binary splitting (SPLIT_BT_HOR).
  • the vertical binary division (SPLIT_BT_VER) means division in which the current CU is divided into two in the vertical direction. As shown in FIG. 5, two CUs having a height equal to the height of the current CU and a width of half the width of the current CU may be generated by vertical binary division.
  • the horizontal binary division means division in which the current CU is divided into two in the horizontal direction. As shown in FIG. 5, two CUs having a height of half the height of the current CU and a width equal to the width of the current CU may be generated by horizontal binary division.
  • the two divisions according to the ternary tree structure may include vertical ternary splitting (SPLIT_TT_VER) and horizontal ternary splitting (hotizontal ternary splitting, SPLIT_TT_HOR).
  • the vertical ternary division (SPLIT_TT_VER) divides the current CU in the vertical direction at a ratio of 1:2:1. As shown in FIG. 5, by vertical ternary division, two CUs having a height equal to the height of the current CU and a width of 1/4 of the width of the current CU, and a current CU having a height equal to the height of the current CU A CU with a width of half the width of can be created.
  • the horizontal ternary division divides the current CU in the horizontal direction at a ratio of 1:2:1. As shown in FIG. 4, by horizontal ternary division, two CUs having a height of 1/4 of the height of the current CU and having the same width as the width of the current CU, and a height of half the height of the current CU, and the current One CU can be created with a width equal to the width of the CU.
  • FIG. 6 is a diagram illustrating a signaling mechanism of block division information in a quadtree with nested multi-type tree structure according to the present disclosure.
  • the CTU is treated as a root node of a quadtree, and the CTU is first divided into a quadtree structure.
  • Information eg, qt_split_flag
  • qt_split_flag a first value (eg, “1”)
  • the current CU may be quadtree split.
  • qt_split_flag is a second value (eg, "0")
  • the current CU is not divided into a quadtree, but becomes a leaf node (QT_leaf_node) of the quadtree.
  • the leaf nodes of each quadtree can then be further divided into a multi-type tree structure. That is, a leaf node of a quad tree may be a node (MTT_node) of a multi-type tree.
  • a first flag (ex. mtt_split_cu_flag) may be signaled to indicate whether the current node is additionally divided.
  • a second flag (e.g. mtt_split_cu_verticla_flag) may be signaled to indicate the splitting direction.
  • the division direction may be a vertical direction
  • the second flag is 0, the division direction may be a horizontal direction.
  • a third flag (eg, mtt_split_cu_binary_flag) may be signaled to indicate whether the division type is a binary division type or a ternary division type.
  • the division type may be a binary division type
  • the third flag when the third flag is 0, the division type may be a ternary division type.
  • Nodes of a multitype tree obtained by binary division or ternary division may be further partitioned into a multitype tree structure.
  • nodes of a multitype tree cannot be partitioned into a quadtree structure.
  • the first flag is 0, the corresponding node of the multi-type tree is no longer divided and becomes a leaf node (MTT_leaf_node) of the multi-type tree.
  • the CU corresponding to the leaf node of the multitype tree may be used as the above-described final coding unit.
  • a multi-type tree splitting mode (MttSplitMode) of the CU may be derived as shown in Table 1.
  • the multitree partitioning mode may be abbreviated as a multitree partitioning type or a partitioning type.
  • a bold block edge 710 represents a quadtree division
  • the remaining edges 720 represent a multitype tree division.
  • the CU may correspond to a coding block (CB).
  • a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.
  • the chroma component (sample) CB or TB size is determined by the luma component (sample) according to the component ratio according to the color format (chroma format, ex. 4:4:4, 4:2:2, 4:2:0, etc.) of the picture/video. ) Can be derived based on CB or TB size.
  • the color format is 4:4:4, the chroma component CB/TB size may be set equal to the luma component CB/TB size.
  • the width of the chroma component CB/TB may be set to half the width of the luma component CB/TB, and the height of the chroma component CB/TB may be set to the height of the luma component CB/TB.
  • the width of the chroma component CB/TB may be set to half the width of the luma component CB/TB, and the height of the chroma component CB/TB may be set to half the height of the luma component CB/TB.
  • the size of the CU when the size of the CTU is 128 based on the luma sample unit, the size of the CU may have a size from 128 x 128 to 4 x 4, which is the same size as the CTU. In one embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size may have a size ranging from 64x64 to 2x2.
  • the CU size and the TU size may be the same.
  • a plurality of TUs may exist in the CU region.
  • the TU size may generally represent a luma component (sample) TB (Transform Block) size.
  • the TU size may be derived based on a preset maximum allowable TB size (maxTbSize). For example, when the CU size is larger than the maxTbSize, a plurality of TUs (TB) having the maxTbSize may be derived from the CU, and transformation/inverse transformation may be performed in units of the TU (TB). For example, the maximum allowable luma TB size may be 64x64, and the maximum allowable chroma TB size may be 32x32. If the width or height of the CB divided according to the tree structure is larger than the maximum transform width or height, the CB may be automatically (or implicitly) divided until the TB size limit in the horizontal and vertical directions is satisfied.
  • the intra prediction mode/type is derived in units of the CU (or CB), and procedures for deriving neighboring reference samples and generating prediction samples may be performed in units of TU (or TB).
  • the intra prediction mode/type is derived in units of the CU (or CB)
  • procedures for deriving neighboring reference samples and generating prediction samples may be performed in units of TU (or TB).
  • one or a plurality of TUs (or TBs) may exist in one CU (or CB) region, and in this case, the plurality of TUs (or TBs) may share the same intra prediction mode/type.
  • the following parameters may be signaled from the encoding device to the decoding device as SPS syntax elements.
  • SPS syntax elements For example, CTU size, a parameter indicating the size of the root node of a quadtree tree, MinQTSize, a parameter indicating the minimum usable size of a quadtree leaf node, MaxBTSize, a parameter indicating the maximum usable size of a binary tree root node, and a ternary tree.
  • MaxTTSize a parameter representing the maximum usable size of a root node, MaxMttDepth, a parameter representing the maximum allowed hierarchy depth of a multitype tree divided from a quadtree leaf node, and a parameter representing the minimum usable leaf node size of a binary tree.
  • MinBtSize and MinTtSize which is a parameter indicating the minimum available leaf node size of the ternary tree, may be signaled.
  • the CTU size may be set to a 128x128 luma block and two 64x64 chroma blocks corresponding to the luma block.
  • MinQTSize is set to 16x16
  • MaxBtSize is set to 128x1208
  • MaxTtSzie is set to 64x64
  • MinBtSize and MinTtSize are set to 4x4
  • MaxMttDepth may be set to 4.
  • Quart tree partitioning can be applied to CTU to create quadtree leaf nodes.
  • the quadtree leaf node may be referred to as a leaf QT node.
  • Quadtree leaf nodes may have a size of 128x128 (e.g.
  • the leaf QT node is 128x128, it may not be additionally divided into a binary tree/ternary tree. This is because in this case, even if it is divided, it exceeds MaxBtsize and MaxTtszie (i.e. 64x64). In other cases, the leaf QT node can be further divided into a multi-type tree. Therefore, the leaf QT node is a root node for a multi-type tree, and the leaf QT node may have a multi-type tree depth (mttDepth) of 0. If the multi-type tree depth reaches MaxMttdepth (ex. 4), additional partitioning may not be considered any more.
  • mttDepth multi-type tree depth
  • the encoding apparatus may omit signaling of the division information. In this case, the decoding apparatus may derive the segmentation information with a predetermined value.
  • one CTU may include a coding block of luma samples (hereinafter referred to as a “luma block”) and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as a “chroma block”).
  • the above-described coding tree scheme may be applied equally to the luma block and the chroma block of the current CU, or may be applied separately.
  • a luma block and a chroma block in one CTU may be divided into the same block tree structure, and the tree structure in this case may be represented as a single tree (SINGLE_TREE).
  • a luma block and a chroma block in one CTU may be divided into individual block tree structures, and the tree structure in this case may be represented as a dual tree (DUAL_TREE). That is, when the CTU is divided into a dual tree, a block tree structure for a luma block and a block tree structure for a chroma block may exist separately.
  • the block tree structure for the luma block may be referred to as a dual tree luma (DUAL_TREE_LUMA)
  • the block tree structure for the chroma block may be referred to as a dual tree chroma (DUAL_TREE_CHROMA).
  • luma blocks and chroma blocks in one CTU may be limited to have the same coding tree structure.
  • luma blocks and chroma blocks may have separate block tree structures from each other. If an individual block tree structure is applied, a luma coding tree block (CTB) may be divided into CUs based on a specific coding tree structure, and the chroma CTB may be divided into chroma CUs based on a different coding tree structure.
  • CTB luma coding tree block
  • a CU in an I slice/tile group to which an individual block tree structure is applied is composed of a coding block of a luma component or a coding block of two chroma components, and a CU of a P or B slice/tile group has three color components (luma component And two chroma components).
  • the structure in which the CU is divided is not limited thereto.
  • the BT structure and the TT structure can be interpreted as a concept included in the Multiple Partitioning Tree (MPT) structure, and the CU can be interpreted as being divided through the QT structure and the MPT structure.
  • MPT Multiple Partitioning Tree
  • a syntax element e.g., MPT_split_type
  • MPT_split_mode a syntax element including information on which direction of splitting between horizontal and horizontal.
  • the CU may be divided in a different way from the QT structure, the BT structure, or the TT structure. That is, according to the QT structure, the CU of the lower depth is divided into 1/4 size of the CU of the upper depth, or the CU of the lower depth is divided into 1/2 of the CU of the upper depth according to the BT structure, or according to the TT structure. Unlike CUs of lower depth are divided into 1/4 or 1/2 of CUs of higher depth, CUs of lower depth are 1/5, 1/3, 3/8, 3 of CUs of higher depth depending on the case. It may be divided into /5, 2/3, or 5/8 size, and the method of partitioning the CU is not limited thereto.
  • the quadtree coding block structure accompanying the multi-type tree can provide a very flexible block division structure.
  • different partitioning patterns may potentially lead to the same coding block structure result in some cases.
  • the encoding device and the decoding device can reduce the amount of data of the split information by limiting the occurrence of such redundant split patterns.
  • FIG. 8 exemplarily shows redundant partitioning patterns that may occur in binary tree partitioning and ternary tree partitioning.
  • consecutive binary divisions 810 and 820 in one direction of the second level have the same coding block structure as binary division for the center partition after ternary division.
  • the binary tree division for the center blocks 830 and 840 of the ternary tree division may be prohibited. This prohibition can be applied to CUs of all pictures.
  • signaling of corresponding syntax elements may be modified to reflect such a prohibited case, and through this, the number of bits signaled for division may be reduced. For example, as in the example shown in FIG.
  • the mtt_split_cu_binary_flag syntax element indicating whether the division is binary division or ternary division is not signaled, and its value is It can be induced to 0 by the decoding device.
  • the source or coded picture/video may include a luma component (Y) block and two chroma component (cb, cr) blocks. That is, one pixel of a picture/image may include a luma sample and two chroma samples cb and cr.
  • the chroma format may represent a configuration format of a luma sample and a chroma sample (cb, cr), and may also be called a color format.
  • the chroma format may be predetermined or may be signaled adaptively. For example, the chroma format may be signaled based on at least one of chroma_format_idc and separate_colour_plane_flag as shown in Table 2.
  • At least one of chroma_format_idc and separate_colour_plane_flag may be signaled through a higher level syntax such as DPS, VPS, SPS, or PPS.
  • chroma_format_idc and separate_colour_plane_flag may be included in the SPS syntax.
  • chroma_format_idc may indicate a luma sample and a format of a chroma sample corresponding thereto, and separate_colour_plane_flag indicates whether three color components (Y, Cb, Cr) are separately encoded in a 4:4:4 chroma format. Can be indicated.
  • the chroma format corresponds to a monochrome format, and the current block does not include a chroma component block and may include only a luma component block.
  • chroma_format_idc 1
  • the chroma format corresponds to a 4:2:0 chroma format
  • the width and height of the chroma component block may correspond to half of the width and height of the luma component block, respectively.
  • the chroma format corresponds to the 4:2:2 chroma format
  • the width of the chroma component block is half the width of the luma component block
  • the height of the chroma component block is equal to the height of the luma component block. It can be the same.
  • the chroma format corresponds to a 4:4:4 chroma format
  • the width and height of the chroma component block may be the same as the width and height of the luma component block, respectively.
  • SubWidthC and SubHeightC may represent a ratio between a luma sample and a chroma sample.
  • the width and height of the luma component block are CbWidth and CbHeight, respectively
  • the width and height of the chroma component block may be derived as (CbWidth/SubwidthC) and (CbHeight/SubHeightC), respectively.
  • the size of a chroma block may have a great influence on throughput. For example, when a chroma block having a predetermined size or less is excessively generated, a throughput of an image encoding/decoding process may be significantly lowered. In order to solve this problem, CU partitioning may be limited so that chroma blocks of a predetermined size or less are not generated.
  • the image encoding/decoding apparatus may set a minimum size of a chroma block.
  • a chroma block may be limited to include at least 16 chroma samples.
  • division of a luma block or a chroma block may be limited so that a 2x2, 2x4, or 4x2 chroma block is not generated.
  • quadtree division and/or binary division for 2x8, 4x4, or 8x2 chroma blocks may be limited.
  • ternary division for 2x8, 2x16, 4x4, 4x8, 8x2, or 8x4 chroma blocks may be limited.
  • quadtree division for the current block may be limited.
  • binary division for the current block may be restricted.
  • ternary division for the current block may be limited.
  • a luma block and a chroma block corresponding to the luma block may be divided in the same manner.
  • a chroma block corresponding to the luma block may also be vertically ternary segmented.
  • whether to divide a CU may be determined based on the size of a luma block included in the CU.
  • the size of the chroma block corresponding to the luma block may be determined based on the size and color format of the luma block, as described above with reference to Table 2.
  • FIG. 9 is a diagram illustrating an example of a luma block and a chroma block in a 4:2:0 color format.
  • 10A to 10C are diagrams illustrating an example of a syntax for dividing a current CTU into a local dual tree.
  • the size of a chroma block corresponding to the luma block may be determined to be 8x4.
  • the 8x4 chroma block is vertically ternary divided, a 2x4 chroma block may be generated.
  • the chroma block is limited to include at least 16 chroma samples, the 2x4 chroma block cannot satisfy the minimum size limit. Accordingly, additional division of an 8x4 chroma block may be prohibited in the 4:2:0 color format.
  • the additional division of the chroma block may be allowed. Accordingly, when additional partitioning is performed only on the luma block, the luma block and the chroma block that have been divided into a single tree structure in the current CTU may be converted into a dual tree structure.
  • a luma block divided into a dual tree structure and a divided structure of a chroma block may be referred to as a local dual tree structure.
  • 10A to 10C are diagrams illustrating an example of syntax for converting a single tree structure to a dual tree structure.
  • 10A to 10C illustrate one coding_tree syntax by dividing it into three drawings for convenience.
  • a prediction mode type of each of CUs generated from a current CTU may be determined based on a modeTypeCondition parameter in a coding_tree syntax.
  • modeTypeCondition may indicate a prediction mode characteristic of each of the CUs.
  • modeType may indicate a prediction mode type of each of the CUs.
  • modeType is MODE_TYPE_ALL indicating that all prediction modes such as intra prediction, IBC, palette mode, inter prediction, etc. are available, MODE_TYPE_INTRA indicating that only intra prediction, IBC and palette modes are available, and only inter prediction modes are available. It can have any one of MODE_TYPE_INTER indicating that it is.
  • the modeTypeCondition of the current CU may have any one of a first value (e.g. 0) to a third value (e.g. 2) according to a predetermined condition.
  • modeTypeCondition may have a first value (e.g. 0).
  • the modeTypeCondition may have a second value (e.g. 1).
  • the current CU may mean a luma component block of the current CU.
  • the modeTypeCondition is the second value (eg 1) or the second value according to whether the current CU is included in the I slice. It can have a value of 3 (eg 2).
  • modeTypeCondition has a second value if the current CU is included in the I slice, and modeTypeCondition is zero if the current CU is not included in the I slice. It can have a value of 3.
  • the current CU may mean a luma component block of the current CU.
  • modeTypeCondition may have a first value (e.g. 0).
  • the modeType of the current CU may be determined based on the value of modeTypeCondition.
  • modeTypeCondition has a second value (e.g. 1) (1010)
  • modeType may be determined as MODE_TYPE_INTRA (1020).
  • modeType when modeTypeCondition has a third value (e.g. 2) (1030), modeType may be determined based on the value of mode_constraint_flag.
  • mode_constraint_flag may indicate whether the inter prediction mode can be applied to the current CU.
  • the first value (e.g. 0) of mode_constraint_flag may indicate that only the inter prediction mode can be applied to the current CU.
  • the modeType of the current CU may be determined as MODE_TYPE_INTER.
  • the second value (e.g. 1) of mode_constraint_flag may indicate that the inter prediction mode cannot be applied to the current CU.
  • modeType may be determined as MODE_TYPE_INTRA (1040).
  • modeTypeCondition has a value other than the second value (eg 1) and the third value (eg 2) (for example, when modeTypeCondition has the first value (eg 0))
  • modeType is the same value as modeTypeCurr It can be determined as (1050).
  • modeTypeCurr is a call input value of the coding_tree syntax, and may mean a prediction mode type of the current CU.
  • modeTypeCurr may be MODE_TYPE_ALL.
  • the modeType determined based on the value of modeTypeCondition may be used as a call input value of a coding_tree syntax for calling a lower CU obtained by dividing the current CU.
  • a treeType of a lower CU generated by dividing the current CU may be determined (1060 ).
  • the split structure of the lower CU may be determined as a dual tree luma (DUAL_TREE_LUMA).
  • the partition structure of the lower CU may be the same as the partition structure of the current CU (treeTypeCurr).
  • Information on the partition structure of the lower CU may be stored in the parameter treeType.
  • the treeType and modeType can be used as input values of coding_tree syntax for calling lower CUs by additionally dividing the current CU.
  • the current CU may be additionally divided into a dual tree structure.
  • the lower CU may have a tree structure of a dual tree luma (DUAL_TREE_LUMA). That is, the luma component and the chroma component of the current CU may be divided into separate tree structures (1070).
  • DUAL_TREE_LUMA dual tree luma
  • the chroma component of the current CU is not divided, and the lower CU may have a tree structure of a dual tree chroma (DUAL_TREE_CHROMA). Yes (1080).
  • the modeType of the lower CU may be determined based on modeTypeCondition.
  • the modeType of the lower CU is MODE_TYPE_INTRA
  • the luma component of the lower CU may have a dual tree luma tree structure
  • the chroma component of the lower CU may have a dual tree chroma tree structure. That is, the lower CU partially has a dual tree structure in the current CTU, and such a partition structure may be referred to as a local dual tree structure.
  • Intra prediction may represent prediction of generating prediction samples for a current block based on reference samples in a picture (hereinafter, referred to as a current picture) to which the current block belongs.
  • a current picture a picture to which the current block belongs.
  • neighboring reference samples to be used for intra prediction of the current block may be derived.
  • the neighboring reference samples of the current block are a sample adjacent to the left boundary of the current block of size nWxnH, a total of 2xnH samples adjacent to the bottom-left, and a sample adjacent to the top boundary of the current block. And a total of 2xnW samples adjacent to the top-right side and one sample adjacent to the top-left side of the current block.
  • the peripheral reference samples of the current block may include a plurality of columns of upper peripheral samples and a plurality of rows of left peripheral samples.
  • the neighboring reference samples of the current block are a total of nH samples adjacent to the right boundary of the current block of size nWxnH, a total of nW samples adjacent to the bottom boundary of the current block, and the lower right side of the current block. It may include one sample adjacent to (bottom-right).
  • the decoder may construct neighboring reference samples to be used for prediction by substituting samples that are not available with available samples.
  • neighboring reference samples to be used for prediction may be configured through interpolation of available samples.
  • a prediction sample can be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) neighboring reference samples of the current block Among them, the prediction sample may be derived based on a reference sample existing in a specific (prediction) direction with respect to the prediction sample.
  • it may be called a non-directional mode or a non-angular mode
  • it may be called a directional mode or an angular mode.
  • LIP linear interpolation intra prediction
  • chroma prediction samples may be generated based on luma samples using a linear model. This case may be called LM (Linear Model) mode.
  • LM Linear Model
  • a temporary prediction sample of the current block is derived based on the filtered surrounding reference samples, and at least one derived according to the intra prediction mode among the existing surrounding reference samples, that is, unfiltered surrounding reference samples.
  • a prediction sample of the current block may be derived by weighted summation of a reference sample and the temporary prediction sample. This case may be called PDPC (Position dependent intra prediction).
  • a reference sample line having the highest prediction accuracy among the neighboring multi-reference sample lines of the current block may be selected, and a prediction sample may be derived using a reference sample positioned in the prediction direction from the corresponding line.
  • information on the used reference sample line eg, intra_luma_ref_idx
  • MRL multi-reference line intra prediction
  • the current block may be divided into vertical or horizontal subpartitions, and intra prediction may be performed for each subpartition based on the same intra prediction mode.
  • neighboring reference samples for intra prediction may be derived for each subpartition. That is, the reconstructed sample of the previous sub-partition in the encoding/decoding order may be used as a neighboring reference sample of the current sub-partition.
  • the intra prediction mode for the current block is equally applied to the subpartitions, but by deriving and using neighboring reference samples in units of the subpartitions, intra prediction performance may be improved in some cases.
  • This prediction method may be called intra sub-partitions (ISP) or ISP-based intra prediction.
  • the intra prediction technique may include at least one of the aforementioned LIP, LM, PDPC, MRL, and ISP. Meanwhile, post-processing filtering may be performed on the derived prediction samples as necessary.
  • the intra prediction procedure may include an intra prediction mode/type determination step, a neighbor reference sample derivation step, and an intra prediction mode/type-based prediction sample derivation step. Also, if necessary, a post-filtering step may be performed on the derived prediction samples.
  • FIG. 11 is a flowchart illustrating a video/video encoding method based on intra prediction.
  • the encoding method of FIG. 11 may be performed by the video encoding apparatus of FIG. 2. Specifically, step S1110 may be performed by the intra prediction unit 185, and step S1120 may be performed by the residual processing unit. Specifically, step S1120 may be performed by the subtraction unit 115. Step S1130 may be performed by the entropy encoding unit 190.
  • the prediction information of step S1130 may be derived by the intra prediction unit 185, and the residual information of step S1130 may be derived by the residual processing unit.
  • the residual information is information on the residual samples.
  • the residual information may include information on quantized transform coefficients for the residual samples.
  • the residual samples may be derived as transform coefficients through the transform unit 120 of the image encoding apparatus, and the transform coefficients may be derived as quantized transform coefficients through the quantization unit 130.
  • Information on the quantized transform coefficients may be encoded by the entropy encoding unit 190 through a residual coding procedure.
  • the image encoding apparatus may perform intra prediction on the current block (S1110).
  • the video encoding apparatus determines the intra prediction mode/type for the current block, derives neighboring reference samples of the current block, and then generates prediction samples in the current block based on the intra prediction mode/type and the neighboring reference samples. can do.
  • the procedure of determining the intra prediction mode/type, deriving neighboring reference samples, and generating prediction samples may be performed simultaneously, or one procedure may be performed before the other procedure.
  • FIG. 12 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • the intra prediction unit 185 of the video encoding apparatus may include an intra prediction mode/type determination unit 186, a reference sample derivation unit 187, and/or a prediction sample derivation unit 188.
  • the intra prediction mode/type determiner 186 may determine an intra prediction mode/type for the current block.
  • the reference sample derivation unit 187 may derive neighboring reference samples of the current block.
  • the prediction sample derivation unit 188 may derive prediction samples of the current block.
  • the intra prediction unit 185 may further include a prediction sample filter unit (not shown).
  • the image encoding apparatus may determine a mode/type applied to the current block from among a plurality of intra prediction modes/types.
  • the video encoding apparatus may compare RD costs for the intra prediction modes/types and determine an optimal intra prediction mode/type for the current block.
  • the image encoding apparatus may perform a prediction sample filtering procedure.
  • Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.
  • the apparatus for encoding an image may generate residual samples for the current block based on prediction samples or filtered prediction samples (S1120).
  • the image encoding apparatus may derive the residual samples by subtracting the prediction samples from original samples of the current block. That is, the image encoding apparatus may derive the residual sample value by subtracting the corresponding predicted sample value from the original sample value.
  • the image encoding apparatus may encode image information including information about the intra prediction (prediction information) and residual information about the residual samples (S1130).
  • the prediction information may include intra prediction mode information and/or intra prediction technique information.
  • the image encoding apparatus may output the encoded image information in the form of a bitstream.
  • the output bitstream may be delivered to an image decoding apparatus through a storage medium or a network.
  • the residual information may include a residual coding syntax to be described later.
  • the image encoding apparatus may transform/quantize the residual samples to derive quantized transform coefficients.
  • the residual information may include information on the quantized transform coefficients.
  • the image encoding apparatus may generate a reconstructed picture (including reconstructed samples and a reconstructed block). To this end, the image encoding apparatus may perform inverse quantization/inverse transformation on the quantized transform coefficients again to derive (modified) residual samples. The reason why the residual samples are transformed/quantized and then inverse quantized/inverse transformed is performed to derive residual samples that are the same as the residual samples derived from the image decoding apparatus.
  • the image encoding apparatus may generate a reconstructed block including reconstructed samples for the current block based on the prediction samples and the (modified) residual samples. A reconstructed picture for the current picture may be generated based on the reconstructed block. As described above, an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
  • FIG. 13 is a flowchart illustrating a video/video decoding method based on intra prediction.
  • the image decoding apparatus may perform an operation corresponding to an operation performed by the image encoding apparatus.
  • the decoding method of FIG. 13 may be performed by the video decoding apparatus of FIG. 3.
  • Steps S1310 to S1330 may be performed by the intra prediction unit 265, and the prediction information of step S1310 and the residual information of step S1440 may be obtained from the bitstream by the entropy decoding unit 210.
  • the residual processing unit of the image decoding apparatus may derive residual samples for the current block based on the residual information (S1340).
  • the inverse quantization unit 220 of the residual processing unit derives transform coefficients by performing inverse quantization based on the quantized transform coefficients derived based on the residual information
  • the inverse transform unit of the residual processing unit ( 230) may derive residual samples for the current block by performing inverse transform on the transform coefficients.
  • Step S1350 may be performed by the addition unit 235 or the restoration unit.
  • the image decoding apparatus may derive an intra prediction mode/type for the current block based on the received prediction information (intra prediction mode/type information) (S1310).
  • the image decoding apparatus may derive neighboring reference samples of the current block (S1320).
  • the image decoding apparatus may generate prediction samples in the current block based on the intra prediction mode/type and the neighboring reference samples (S1330).
  • the image decoding apparatus may perform a prediction sample filtering procedure. Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.
  • the image decoding apparatus may generate residual samples for the current block based on the received residual information (S1340).
  • the image decoding apparatus may generate reconstructed samples for the current block based on the prediction samples and the residual samples, and derive a reconstructed block including the reconstructed samples (S1350).
  • a reconstructed picture for the current picture may be generated based on the reconstructed block.
  • an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
  • FIG. 14 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • the intra prediction unit 265 of the image decoding apparatus may include an intra prediction mode/type determination unit 266, a reference sample derivation unit 267, and a prediction sample derivation unit 268. .
  • the intra prediction mode/type determiner 266 determines an intra prediction mode/type for the current block based on intra prediction mode/type information generated and signaled by the intra prediction mode/type determiner 186 of the image encoding apparatus.
  • the reference sample deriving unit 266 may derive neighboring reference samples of the current block from the reconstructed reference region in the current picture.
  • the prediction sample derivation unit 268 may derive prediction samples of the current block.
  • the intra prediction unit 265 may further include a prediction sample filter unit (not shown).
  • the intra prediction mode information may include flag information (eg intra_luma_mpm_flag and/or intra_chroma_mpm_flag) indicating whether a most probable mode (MPM) is applied to the current block or a remaining mode is applied, for example. And, when the MPM is applied to the current block, the intra prediction mode information may further include index information (eg intra_luma_mpm_idx and/or intra_chroma_mpm_idx) indicating one of intra prediction mode candidates (MPM candidates).
  • the intra prediction mode candidates (MPM candidates) may be composed of an MPM candidate list or an MPM list.
  • the intra prediction mode information includes remaining mode information indicating one of the remaining intra prediction modes except for the intra prediction mode candidates (MPM candidates) (eg intra_luma_mpm_remainder and/ Alternatively, intra_chroma_mpm_remainder) may be further included.
  • the video decoding apparatus may determine an intra prediction mode of the current block based on the intra prediction mode information.
  • the MPM candidate modes may include an intra prediction mode and additional candidate modes of a neighboring block (e.g. a left neighboring block and/or an upper neighboring block) of the current block.
  • the intra prediction mode may include two non-directional intra prediction modes and 33 directional intra prediction modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode, and the directional intra prediction modes may include intra prediction modes 2 to 34.
  • the planar intra prediction mode may be referred to as a planner mode, and the DC intra prediction mode may be referred to as a DC mode.
  • the intra prediction mode may include two non-directional intra prediction modes and 65 extended directional intra prediction modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode
  • the extended directional intra prediction modes may include intra prediction modes 2 to 66.
  • the intra prediction mode can be applied to blocks of all sizes, and can be applied to both a luma component (a luma block) and a chroma component (a chroma block).
  • the intra prediction mode may include two non-directional intra prediction modes and 129 directional intra prediction modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode, and the directional intra prediction modes may include 2 to 130 intra prediction modes.
  • the intra prediction mode may further include a cross-component linear model (CCLM) mode for chroma samples in addition to the aforementioned intra prediction modes.
  • CCLM cross-component linear model
  • the CCLM mode can be divided into L_CCLM, T_CCLM, and LT_CCLM depending on whether left samples are considered, upper samples are considered, or both are considered to derive LM parameters, and can be applied only to a chroma component.
  • the intra prediction mode may include 93 directional intra prediction modes along with two non-directional intra prediction modes in order to capture an arbitrary edge direction presented in a natural video.
  • Non-directional intra prediction modes may include planar mode and DC mode.
  • the planar mode may be indicated as INTRA_PLANAR
  • the DC mode may be indicated as INTRA_DC.
  • the directional intra prediction mode may be expressed as INTRA_ANGULAR-14 to INTRA_ANGULAR-1, and INTRA_ANGULAR2 to INTRA_ANGULAR80.
  • the intra prediction technique information may be implemented in various forms.
  • the intra prediction technique information may include intra prediction technique index information indicating one of a plurality of intra prediction techniques.
  • the intra prediction technique information includes reference sample line information (eg intra_luma_ref_idx) indicating whether the MRL is applied to the current block and, if applied, a reference sample line (eg intra_luma_ref_idx), and the ISP is applied to the current block.
  • ISP flag information indicating whether it is applied (eg intra_subpartitions_mode_flag), ISP type information indicating the split type of subpartitions when the ISP is applied (eg intra_subpartitions_split_flag), flag information indicating whether or not PDPC is applied, or indicating whether the LIP is applied. It may include at least one of flag information.
  • the ISP flag information may be referred to as an ISP application indicator.
  • the intra prediction mode information and/or the intra prediction technique information may be encoded/decoded using the coding method described in the present disclosure.
  • the intra prediction mode information and/or the intra prediction method information may be encoded/decoded through entropy coding (e.g. CABAC, CAVLC) based on a truncated (rice) binary code.
  • entropy coding e.g. CABAC, CAVLC
  • intra prediction When intra prediction is performed on the current block, prediction on a luma component block (luma block) of the current block and prediction on a chroma component block (chroma block) may be performed.
  • the intra prediction mode for the chroma block is It can be set separately from the intra prediction mode for the luma block.
  • an intra prediction mode for a chroma block may be indicated based on intra chroma prediction mode information, and the intra chroma prediction mode information may be signaled in the form of an intra_chroma_pred_mode syntax element.
  • the intra-chroma prediction mode information includes one of a planar mode, a DC mode, a vertical mode, a horizontal mode, a derived mode (DM), and a cross-component linear model (CCLM) mode.
  • the planar mode may indicate a 0th intra prediction mode
  • the DC mode may indicate a 1st intra prediction mode
  • the vertical mode may indicate a 26th intra prediction mode
  • the horizontal mode may indicate a 10th intra prediction mode.
  • DM can also be called direct mode.
  • CCLM may be referred to as a linear model (LM).
  • the DM and CCLM are dependent intra prediction modes that predict a chroma block using information of a luma block.
  • the DM may represent a mode in which an intra prediction mode identical to an intra prediction mode for the luma component is applied as an intra prediction mode for the chroma component.
  • the CCLM subsamples the reconstructed samples of the luma block in the process of generating the prediction block for the chroma block, and then applies CCLM parameters ⁇ and ⁇ to the subsampled samples to be derived as shown in Equation 1. It may represent an intra prediction mode in which samples are used as prediction samples of the chroma block.
  • pred c (i,j) may represent a predicted sample of (i,j) coordinates of the current chroma block in the current CU.
  • rec L '(i,j) may represent a reconstructed sample of the (i,j) coordinate of the current luma block in the CU.
  • rec L '(i,j) may represent a down-sampled reconstructed sample of the current luma block.
  • the linear model coefficients ⁇ and ⁇ may be signaled, but may also be derived from surrounding samples.
  • the intra prediction mode of the chroma block may be derived as the intra prediction mode of the corresponding luma block.
  • an intra prediction mode at a predetermined position of a corresponding luma block may be used as an intra prediction mode of a chroma block.
  • intra prediction of a chroma block may be performed using Multiple Direct Modes (MDM).
  • MDM Multiple Direct Modes
  • the multiple DM is a mode in which the above-described single DM is extended to a plurality of modes, and a DM candidate list including a plurality of DM candidates is constructed to induce an intra prediction mode of a chroma block, and is included in the DM candidate list.
  • One of the candidates may be derived as an intra prediction mode of a chroma block.
  • the DM candidate list may include at least one of a plurality of DM candidates below.
  • -Directional mode derived by adding or subtracting a predetermined offset (e.g. 1) to the already included directional mode
  • -Default DM candidate mode vertical mode, horizontal mode, 2, 34, 66, 10, 26 modes (in case of 65 directional modes)
  • the intra prediction mode of the chroma block may be derived based on the intra chroma prediction mode information (intra_chroma_pred_mode) and/or the intra prediction mode of the corresponding luma block. For example, when the intra chroma prediction mode information indicates DM, the intra prediction mode of the chroma block may be determined to be the same as the intra prediction mode of the corresponding luma block.
  • intra prediction for a luma block may be performed based on an MPM list, and intra prediction for a chroma block may be performed based on a predetermined default mode and/or DM.
  • the default intra prediction mode may include a planar mode, a DC mode, a vertical mode, and a horizontal mode.
  • the palette mode may represent a prediction mode for encoding/decoding a current block based on a palette (or palette table) including a predetermined representative color value set.
  • each sample in the current block may be represented by a palette index indicating a predetermined representative color value.
  • encoding/decoding using the palette mode may be referred to as palette encoding/decoding.
  • the palette mode may be used to improve encoding/decoding efficiency of a specific image.
  • screen content which is an image that includes a significant amount of text and graphics and is generated by an electronic device such as a computer or a smartphone, includes a local area separated by a sharp edge, and the local area is a relatively small number of It can be expressed as pixel values. Therefore, the palette mode, which expresses most pixel values in the current block with a relatively small number of indices, is more effective in encoding/decoding screen contents than other prediction modes (eg intra prediction mode, inter prediction mode, etc.). I can.
  • the palette mode is a kind of the aforementioned intra prediction mode, and may be referred to as a palette encoding mode, an intra palette mode, an intra palette encoding mode, and the like.
  • the palette mode when the palette mode is applied to the current block, unlike the case of the intra prediction mode, the residual value for the current block may not be signaled separately.
  • the palette mode may be similar to the skip mode described above.
  • the palette mode can be applied to both the luma component and the chroma component of the current block.
  • the palette mode may be applied to the chroma component of the current block.
  • the palette mode can be applied individually to the luma component and the chroma component of the current block.
  • the palette mode may be applied to the chroma component of the current block, or other prediction modes (eg intra prediction mode, inter prediction mode, etc.) ) May be applied.
  • a palette table for the current block may be configured based on the palette predictor.
  • the palette predictor may include one or more palette entries (representative color values) and one or more palette indexes for identifying each of the palette entries.
  • the palette predictor may be initialized to a predetermined value (e.g. 0) at the initial encoding/decoding time of the CTU (or slice) including the current block.
  • the palette predictor may be updated using at least one palette entry used for palette encoding/decoding.
  • the size of the palette predictor reaches a predetermined maximum size (i.e., until the palette predictor contains the maximum number of palette entries allowed), the palette of the previous palette predictor that is not included in the current palette table.
  • An entry may be added to the last position (index) of the palette predictor for the next palette encoding. This may be referred to as pallet stuffing.
  • the palette table may include at least one palette entry included in the palette predictor and at least one palette index for identifying the palette entry.
  • a reuse flag indicating whether the palette entry is included in the palette table may be signaled through a bitstream.
  • the reuse flag having the first value e.g. 0
  • a reuse flag having a second value e.g. 1
  • the reuse flag may be encoded using, for example, run-length coding for a value of 0.
  • the palette table may include at least one new palette entry not included in the palette predictor and at least one palette index for identifying the new palette entry.
  • Information on the new palette entry e.g. total number, component value, etc.
  • a palette index map for a current block to be encoded may be generated. Specifically, a palette index map for the current block by mapping a predetermined palette index in the palette table to each of the plurality of samples based on the similarity between the pixel value and the representative color value of each of the plurality of samples in the current block. Can be generated. In this case, among a plurality of samples in the current block, for a sample (escape sample) having a pixel value similar to a representative color value (palette entry) defined in the palette table, an escape palette index may be mapped. . The escape palette index indicates an escape sample (escape symbol) and may have the largest value in the palette table.
  • whether the current block includes an escape sample may be signaled using an escape sample flag (e.g. palette_escape_val_present_flag).
  • an escape sample flag e.g. palette_escape_val_present_flag
  • a palette_escape_val_present_flag having a first value e.g. 0
  • a palette_escape_val_present_flag having a second value e.g. 1
  • Palette index prediction information about the palette index map may be signaled through a bitstream.
  • the palette index prediction information may include at least one palette index mapped to the current block and run-value information of the palette index.
  • the run-value of the palette index may represent a value obtained by subtracting 1 from the number of palette indices successively mapped to the current block with the same value.
  • the current block includes first to fourth samples continuously present along a predetermined scan direction (eg horizontal direction), and a first palette index (eg 0) in each of the first to third samples
  • a run-value of the first palette index may be 2, and a run-value of the second palette index may be 0.
  • the palette index prediction information may include run-value information of the escape palette index mapped to the escape sample.
  • a palette index map for a current block to be decoded may be generated.
  • a palette index map for the current block may be generated by mapping each of one or more palette indices obtained from the palette index prediction information to each of a plurality of samples in the current block.
  • a value of each of the one or more palette indices may be adjusted based on a last palette index (in mapping order) among one or more palette indices obtained from the palette index prediction information. For example, when the last palette index obtained from the palette index prediction information is an escape palette index, one or more palette entries obtained from the palette index prediction information will be mapped to the current block with a value increased by a predetermined size (eg 1). I can.
  • the current block may be encoded/decoded based on the palette index map. For a sample having a pixel value that is the same as or similar to a representative color value defined in the palette table among a plurality of samples in the current block, a value of a palette index indicating the representative color value may be signaled through a bitstream. Alternatively, for a sample having a pixel value dissimilar to the representative color value defined in the palette table among a plurality of samples in the current block, the quantized pixel value of the sample may be directly signaled through the bitstream.
  • the palette index map may be scanned using a predetermined scan method.
  • the current block may be scanned using a predetermined scan method.
  • 15 is a diagram illustrating an example of a scanning method that can be used in a palette mode.
  • a scan method that can be used in the palette mode may include a horizontal traverse scan and a vertical traverse scan.
  • the horizontal traverse scan may mean a method of scanning odd-numbered rows of the current block (or palette index map) from left to right, and scanning even-numbered rows of the current block from right to left.
  • the vertical traverse scan may mean a method of scanning an odd-numbered column of the current block from top to bottom, and scanning an even-numbered column of the current block from bottom to top.
  • Information about a scan method that can be used in the palette mode may be signaled using a predetermined flag (e.g. palette_transpose_flag).
  • a predetermined flag e.g. palette_transpose_flag
  • a palette_transpose_flag having a first value e.g. 0
  • a palette_transpose_flag having a second value e.g. 1
  • a second value e.g. 1
  • Palette indices mapped to each sample in the current block may be encoded using the'INDEX' mode and the'COPY_ABOVE' mode.
  • the'INDEX' mode and the'COPY_ABOVE' mode may be referred to as a palette sample mode.
  • copy_above_palette_indices_flag e.g copy_above_palette_indices_flag
  • copy_above_palette_indices_flag having a first value may indicate that a predetermined palette index mapped to the current block is encoded using the'INDEX' mode.
  • copy_above_palette_indices_flag having a second value may indicate that a predetermined palette index mapped to the current block is encoded using the'COPY_ABOVE' mode.
  • the value of the palette index can be explicitly signaled through the bitstream.
  • run-value information indicating the number of consecutively encoded samples using the same palette sample mode may be signaled through a bitstream.
  • Palette indices included in the palette index map may be encoded in the following order.
  • the number of palette indexes mapped to the current block (or the current CU) may be signaled.
  • values of each of the palette indices may be signaled using fixed length coding.
  • the number of palette indices and a value of each of the palette indices may be encoded using the bypass mode.
  • bypass bins related to the palette index may be grouped.
  • information on the palette sample mode e.g. copy_above_palette_indices_flag
  • run-value information on the palette sample mode may be signaled in an interleaving manner.
  • component escape values corresponding to escape samples in the current block may be grouped and encoded in bypass mode.
  • At least one additional syntax element (e.g. last_run_type_flag) may be additionally signaled.
  • the signaling process for a run-value corresponding to the last run in the current block may be skipped based on the number of palette indexes and an additional syntax element.
  • 16 is a diagram illustrating an example of a process of encoding a palette of a current block.
  • a plurality of pixels (samples) in a current block may be expressed using a total of three color values (S1610).
  • the first pixels PX1 may have a first color value
  • the second pixels PX2 may have a second color value
  • the third pixels PX3 may have a third color value. .
  • a palette table for the current block may be configured (S1620).
  • the palette table contains palette entries (representative color values) for each color component (eg (G, B, R), (Y, Cb, Cr), etc.) and a palette index (eg 0) for identifying each palette entry. , 1) may be included.
  • the palette table may further include an escape palette index (e.g. 2).
  • the escape palette index may be mapped to an escape sample (or escape symbol) having a pixel value similar to a representative color value defined in the palette table among a plurality of pixels in the current block. For the escape sample to which the escape palette index is mapped, a quantized pixel value of the escape sample may be signaled.
  • a palette index map for the current block is generated by mapping a predetermined palette index in the palette table to each of the plurality of samples based on the similarity between the pixel value and the representative color value of each of the plurality of samples in the current block. It can be done (S1630). For example, a first palette index (eg 0) is mapped to each of the first pixels PX1, a second palette index (eg 1) is mapped to each of the second pixels PX2, and an escape sample The palette index map for the current block may be generated by mapping the escape palette index (eg 2) for the in-third pixel PX3.
  • the palette sample mode and the run-value of the palette sample mode of each of a plurality of samples in the current block can be derived. Yes (S1640, S1650).
  • the palette indexes '1, 0, 1, 1, 1'that are successively mapped to the 3rd row of the palette index map are located at the same position in the 2nd row of the palette index map. Since they have the same index value as the palette indices, they may be encoded in the'COPY_ABOVE' mode, and the run-value of the'COPY_ABOVE' mode may be 4 (S1640).
  • the palette indexes '1, 1, 1'successively mapped to the second row of the palette index map are index values different from the palette indexes existing in the same position of the first row of the palette index map. Since it has an'INDEX' mode, the run-value of the'INDEX' mode may be 2 (S1650). Meanwhile, the escape palette index (e.g. 2) mapped to the third pixel PX3, which is an escape sample, may be encoded in the'INDEX' mode.
  • a palette index map is generated by mapping a predetermined palette index in the palette table to each of the plurality of samples in the current block, and the palette index included in the palette index map is Depending on the scan method, it may be encoded in the'INDEX' mode or the'COPY_ABOVE' mode.
  • FIG. 17 is a diagram illustrating a part of a coding_unit syntax for a palette mode
  • FIGS. 18A to 18E are diagrams showing a palette_coding syntax for a palette mode.
  • the syntax element for the palette mode may be encoded as shown in FIGS. 17 and 18A to 18E and signaled through a bitstream.
  • a palette mode flag pred_mode_plt_flag may indicate whether a palette mode is applied to a current block (or a current CU). For example, a first value (e.g. 0) of pred_mode_plt_flag may indicate that the palette mode is not applied to the current block. Unlike this, the second value (e.g. 1) of pred_mode_plt_flag may indicate that the palette mode is applied to the current block. When pred_mode_plt_flag is not obtained from the bitstream, the value of pred_mode_plt_flag may be determined as the first value.
  • a parameter PredictorPaletteSize[startComp] may indicate the size of a palette predictor for startComp, a first color component of a palette table (current palette table) for a current block.
  • the parameter PalettePredictorEntryReuseFlags[i] may indicate whether the i-th palette entry in the palette predictor is included in the current palette table (ie, reused). For example, PalettePredictorEntryReuseFlags[i] having a first value (e.g. 0) may indicate that the i-th palette entry of the palette predictor is not reused in the current palette table. Alternatively, PalettePredictorEntryReuseFlags[i] having a second value (e.g. 1) may indicate that the i-th palette entry of the palette predictor is reused in the current palette table. In one example, an initial value of PalettePredictorEntryReuseFlags[i] may be set to 0.
  • parameter palette_predictor_run may indicate the number of zeros that exist prior to non-zero palette entries in the PalettePredictorEntryReuseFlags array.
  • parameter num_signalled_palette_entries may indicate the number of palette entries in the current palette table explicitly signaled for the first color component startComp of the current palette table.
  • num_signalled_palette_entries may be inferred as 0.
  • the parameter CurrentPaletteSize[startComp] may indicate the size of the current palette table for the first color component startComp of the current palette table.
  • the value of CurrentPaletteSize[startComp] may be calculated as in Equation 2 below.
  • CurrentPaletteSize[startComp] may have a value between 0 and palette_max_size.
  • parameter new_palette_entries[cIdx][i] may indicate a value of a new palette entry signaled for the i-th color component cIdx.
  • parameter PredictorPaletteEntries[cIdx][i] may indicate the i-th palette entry in the palette predictor for the color component cIdx.
  • parameter CurrentPaletteEntries[cIdx][i] may indicate the i-th palette entry in the current palette table for the color component cIdx.
  • palette_escape_val_present_flag may indicate whether an escape sample (escape symbol) exists. For example, a palette_escape_val_present_flag having a first value (e.g. 0) may indicate that the current block does not include an escape sample. Alternatively, palette_escape_val_present_flag having a second value (e.g. 1) may indicate that the current block includes at least one escape sample. When palette_escape_val_present_flag is not obtained from the bitstream, the value of palette_escape_val_present_flag may be inferred as 1.
  • the parameter MaxPaletteIndex may represent the maximum value of the palette index in the current palette table.
  • the value of MaxPaletteIndex may be calculated as in Equation 3 below.
  • parameter num_palette_indices_minus1 may represent a value obtained by subtracting 1 from the number of palette indices signaled during the palette encoding process of the current block.
  • num_palette_indices_minus1 is not obtained from the bitstream, the value of num_palette_indices_minus1 may be inferred as 0.
  • the parameter palette_idx_idc may be an indicator of a palette index for the current palette table CurrentPaletteEntries.
  • the palette_idx_idc may have a value between 0 and MaxPaletteIndex for the first palette index of the corresponding block, and may have a value between 0 and MaxPaletteIndex-1 for the remaining palette indices of the corresponding block.
  • the value of palette_idx_idc may be inferred as 0.
  • parameter PaletteIndexIdc[i] may indicate the i-th palette_idx_idc. In one example, all values of the array PaletteIndexIdc may be initialized to zero.
  • the parameter copy_above_indices_for_final_run_flag may indicate whether the palette index of the last position in the current block is copied from the previous palette index. For example, copy_above_indices_for_final_run_flag having a first value (e.g. 0) may indicate that the palette index of the last position in the current block is copied from PaletteIndexIdc[num_palette_indices_minus1]. Alternatively, copy_above_indices_for_final_run_flag having a second value (e.g 1) may indicate that the palette index at the last position in the current block is copied from the palette index of the surrounding samples.
  • a first value e.g. 0
  • copy_above_indices_for_final_run_flag having a second value e.g 1
  • the surrounding sample When the vertical traverse scan is used, the surrounding sample may be a sample present at the same position as the current sample in a left column of the current sample. When the horizontal traverse scan is used, the surrounding sample may be a sample present at the same position as the current sample in a row above the current sample.
  • copy_above_indices_for_final_run_flag When copy_above_indices_for_final_run_flag is not obtained from the bitstream, the value of copy_above_indices_for_final_run_flag may be inferred as 0.
  • the parameter palette_transpose_flag may indicate the scanning method of the current block (or palette index map). For example, a palette_transpose_flag having a first value (e.g. 0) may indicate that a horizontal traverse scan is applied to the current block. Unlike this, palette_transpose_flag having a second value (e.g. 1) may indicate that a vertical traverse scan is applied to the current block.
  • a palette_transpose_flag having a first value (e.g. 0) may indicate that a horizontal traverse scan is applied to the current block.
  • palette_transpose_flag having a second value e.g. 1
  • the value of the palette_transpose_flag may be inferred as 0.
  • the parameter copy_above_palette_indices_flag may indicate an encoding mode (palette sample mode) for a current sample in a current block.
  • copy_above_palette_indices_flag having a first value e.g. 0
  • copy_above_palette_indices_flag having a second value e.g. 1
  • CopyAboveIndicesFlag[xC][yC] may indicate an encoding mode for each of a plurality of samples in the current block. That is, CopyAboveIndicesFlag may be an array of copy_above_palette_indices_flag for each of a plurality of samples in the current block.
  • xC and yC may be coordinate indicators indicating a relative position of the current sample from the upper left sample of the current picture.
  • PaletteRunMinus1 When CopyAboveIndicesFlag[xC][yC] has a first value (e.g. 0), PaletteRunMinus1 may represent a value obtained by subtracting 1 from the number of consecutively encoded palette indexes using the'COPY_ABOVE' mode. In contrast, when CopyAboveIndicesFlag[xC][yC] has a second value (e.g. 1), PaletteRunMinus1 may represent a value obtained by subtracting 1 from the number of consecutively encoded palette indexes using the'INDEX' mode.
  • a first value e.g. 0
  • PaletteRunMinus1 When CopyAboveIndicesFlag[xC][yC] has a second value (e.g. 1), PaletteRunMinus1 may represent a value obtained by subtracting 1 from the number of consecutively encoded palette indexes using the'INDEX' mode.
  • the parameter PaletteIndexMap[xC][yC] may indicate a palette index map for a current block. That is, PaletteIndexMap may be an array of CurrentPaletteEntries for each of a plurality of samples in the current block.
  • xC and yC may be coordinate indicators indicating a relative position of the current sample from the upper left sample of the current picture.
  • PaletteIndexMap[xC][yC] may have a value between 0 and (MaxPaletteIndex-1).
  • the parameter PaletteMaxRunMinus1 may represent the maximum value of PaletteRunMinus1. In one example, PaletteMaxRunMinus1 may have a value greater than 0.
  • parameter palette_run_prefix may indicate a prefix part used for binarization of PaletteRunMinus1.
  • parameter palette_run_suffix may indicate a suffix part used for binarization of PaletteRunMinus1.
  • the value of palette_run_suffix may be inferred as 0.
  • PaletteMaxRunMinus1 if the value of PaletteMaxRunMinus1 is 0, the value of PaletteRunMinus1 may be set to 0. Alternatively, if PaletteMaxRunMinus1 is greater than 0, PaletteRunMinus1 may be set based on the value of palette_run_prefix. For example, when the value of palette_run_prefix is less than 2, the value of PaletteRunMinus1 may be set as in Equation 4 below.
  • the value of PaletteRunMinus1 may be calculated as in Equation 5 below.
  • a parameter palette_escape_val may indicate a quantized pixel value of an escape sample in a current block.
  • the parameter PaletteEscapeVal[cIdx][xC][yC] may indicate the quantized pixel value of the escape sample, in which the value of PaletteIndexMap[xC][yC] is MaxPaletteIndex and the value of palette_escape_val_present_flag is 1.
  • cIdx indicates a color component
  • xC and yC may be coordinate indicators indicating a relative position of the current sample from the upper left sample of the current picture.
  • 19 is a diagram illustrating an example of a CU having a local dual tree structure.
  • a current CU may be divided into a quadtree structure for each of a luma component and a chroma component.
  • a 16x16 luma block may be quadtree-divided to generate first to fourth luma blocks 1911 to 1914 each having a size of 8x8.
  • the 8x8 chroma block may be quadtree-divided, so that first to fourth chroma blocks 1921 to 1924 each having a size of 4x4 may be generated.
  • the first chroma block 1921 corresponds to the first luma block 1911
  • the second chroma block 1922 corresponds to the second luma block 1912
  • the third chroma block 1923 is
  • the third luma block 1913 may correspond
  • the fourth chroma block 1924 may correspond to the fourth luma block 1914.
  • the minimum size of the chroma block is limited to include 16 or more chroma samples, additional division of the first to fourth chroma blocks 1921 to 1924 may be prohibited.
  • additional division of the first to fourth luma blocks 1911 to 1914 may be allowed.
  • the third luma block 1913 is vertically binary divided, so that two luma blocks 1913-1 and 1913-2 each having a size of 4x8 may be generated.
  • the division structure of the third luma block 1913 may be referred to as a dual tree luma (DUAL_TREE_LUMA), and the division structure of the third chroma block 1923 may be referred to as a dual tree chroma (DUAL_TREE_CHROMA).
  • the partition structure of the lower CU May be referred to as a local dual tree structure. In this case, an example of a decoding process for the current CU is as shown in FIG. 20.
  • FIG. 20 is a diagram illustrating an example of a decoding process for a current CU in the example of FIG. 19.
  • the luma block and the chroma block of the lower CU having a single tree structure may be decoded based on the same prediction mode (e.g. intra prediction mode, IBC, palette mode, inter prediction mode, etc.).
  • the luma block and the chroma block of a lower CU having a dual tree structure may be individually decoded based on a combination of various prediction modes.
  • a luma block and a chroma block of a lower CU having a dual tree structure may be decoded using the same prediction mode or different prediction modes.
  • FIG. 20 in order to distinguish between a lower CU having a single tree structure and a lower CU having a dual tree structure, only a luma block is shown for a lower CU having a single tree structure, and a luma block for a lower CU having a dual tree structure. And chroma blocks are all shown.
  • a decoding process will be described based on a luma block.
  • a first luma block 1911 having a single tree structure may be decoded using an inter prediction mode.
  • the second luma block 1912 having a single tree structure may be decoded using a palette mode.
  • the fourth luma block 1914 having a single tree structure may be decoded using a palette mode.
  • the 3-1 luma block 1913-1 having a dual tree structure is decoded using the palette mode
  • the 3-2 luma block 1913-2 is decoded using the intra mode
  • the third The chroma block 1923 may be decoded using a palette mode.
  • the decoding process for the first to fourth luma blocks 1911 to 1914 may be sequentially performed.
  • the decoding process for the 3-1 luma block 1913-1 and the 3-2 luma block 1913-2 and the decoding process for the third chroma block 1923 are performed in parallel or in a predetermined order. It can be performed sequentially accordingly.
  • palette decoding for the second luma block 1912 is performed, as described above, one palette predictor including a palette entry for each of the luma component and the chroma component and a palette index for identifying the palette entry is configured. I can. In addition, the palette predictor may be updated using a palette entry applied to the second luma block 1912 for next palette decoding (S2010).
  • the palette decoding for the second luma block 1912 is completed, the palette decoding for the 3-1 luma block 1913-1 and the third chroma block 1923 is performed using the palette predictor updated in step S2010. It can be done individually.
  • the palette predictor for the 3-1 luma block 1913-1 may include only a palette entry for a luma component and a palette index for identifying the palette entry in the palette predictor updated in step S2010 (S2020). .
  • the palette predictor for the 3-1 luma block 1913-1 may be referred to as a luma palette predictor.
  • the luma palette predictor may be updated using the palette entry applied to the 3-1 luma block 1913-1 (S2030). ).
  • the palette predictor for the third chroma block 1923 may include only a palette entry for a chroma component and a palette index for identifying the palette entry in the palette predictor updated in step S2010 (S2040).
  • the palette predictor for the third chroma block 1923 may be referred to as a chroma palette predictor.
  • the chroma palette predictor may be updated using a palette entry applied to the third chroma block 1923 (S2050).
  • palette decoding may be performed on the fourth luma block 1914.
  • the palette predictor for the fourth luma block 1914 may be configured by combining the luma palette predictor updated in step S2030 and the chroma palette predictor updated in step S2050 (S2060). That is, the palette predictor for the fourth luma block 1914 includes a palette entry of a luma component for the 3-1 luma block 1913-1 and a palette entry of a chroma component for the third chroma block 1923, It may include a palette index to identify each palette entry. In this case, the size of the palette predictor for the fourth luma block 1914 (that is, the number of palette entries) may be determined based on the number of palette entries of the luma component.
  • N is an integer greater than 0
  • M is an integer greater than 0
  • the size of the palette predictor for the 4 luma block 1914 may be determined as N. Due to this characteristic, there may be a problem that the palette predictor includes an invalid palette entry or does not include a valid palette entry.
  • 21 and 22 are diagrams for explaining problems that occur when a palette mode is applied to a lower CU having a local dual tree structure in the example of FIG. 20.
  • a luma palette predictor 2110 updated as a result of palette decoding for a 3-1 luma block 1913-1 having a local dual tree structure, with respect to a luma component (eg Y component) may contain 9 palette entries (representative color values).
  • the palette decoding is performed for the fourth luma block 1914 having a single tree structure.
  • the palette predictor 2130 for the fourth luma block 1914 refers to the luma palette predictor 2110 and the chroma palette predictor 2120 based on the size of the luma palette predictor 2110. It can be configured by combining them.
  • the size of the chroma palette predictor 2120 is 2 for each chroma component (eg Cb and Cr).
  • the size of the palette predictor 2130 for the fourth luma block 1914 may be determined to be 9.
  • the palette predictor 2130 for the fourth luma block 1914 may include palette entries 2131 having 7 NULL values for each chroma component. As a result, unnecessary memory space for storing the palette entries 2131 having a NULL value is wasted, and decoding efficiency may be deteriorated.
  • a luma palette predictor 2210 updated as a result of palette decoding for a 3-1 luma block 1913-1 having a local dual tree structure, with respect to a luma component (eg Y) may include three palette entries (representative color values).
  • the palette decoding is performed for the fourth luma block 1914 having a single tree structure.
  • the palette predictor 2230 for the fourth luma block 1914 refers to the luma palette predictor 2210 and the chroma palette predictor 2220 based on the size of the luma palette predictor 2210. It can be configured by combining them.
  • the last two valid palette entries 2221 for each chroma component included in the chroma palette predictor 2220 may be discarded.
  • an optimal palette table for the fourth luma block 1914 cannot be configured, there may be a problem in that the palette decoding performance for the fourth luma block 1914 is deteriorated.
  • a palette predictor is determined based on whether a partition structure of a current block is a local dual tree structure.
  • the updating process may be skipped or the palette mode may be selectively applied.
  • a process of updating a palette predictor may be selectively performed based on a split structure of the current block.
  • FIG. 23 is a flowchart illustrating a palette encoding method according to an embodiment of the present disclosure.
  • the palette encoding method of FIG. 23 may be performed by the image encoding apparatus of FIG. 2. Specifically, steps S2310 to S2350 may be performed by the intra prediction unit 165 or by a separate functional block (e.g. palette encoding unit) different from the intra prediction unit 165.
  • steps S2310 to S2350 may be performed by the intra prediction unit 165 or by a separate functional block (e.g. palette encoding unit) different from the intra prediction unit 165.
  • Whether the palette mode is applied to the current block may be determined based on the prediction mode type of the current block. For example, if the prediction mode type of the current block is a first mode type (eg MODE_TYPE_ALL) to which all of intra prediction, intra block copy (IBC), palette mode, and inter prediction can be applied, the palette mode can be applied to the current block. have. In contrast, when the prediction mode type of the current block is a second mode type to which only intra prediction can be applied (eg MODE_TYPE_INTRA) or a third mode type to which only inter prediction can be applied (eg MODE_TYPE_INTER), the current block is a palette mode. Cannot be applied.
  • a first mode type eg MODE_TYPE_ALL
  • Whether or not the palette mode is applied to the current block may be signaled using a predetermined flag (e.g. pred_mode_plt_flag). For example, when the palette mode is not applied to the current block, a pred_mode_plt_flag having a first value (e.g. 0) may be signaled. In contrast, when the palette mode is applied to the current block, a pred_mode_plt_flag having a second value (e.g. 1) may be signaled.
  • a pred_mode_plt_flag having a first value (e.g. 0) may be signaled.
  • a pred_mode_plt_flag having a second value e.g. 1
  • the image encoding apparatus may configure a palette predictor and a palette table for the current block (S2310).
  • the palette predictor may include at least one palette entry (representative color value) and a palette index for identifying each palette entry.
  • the palette predictor may have a predetermined initial value (e.g. 0).
  • the palette predictor may include at least one palette entry used in a palette encoding process prior to the current block.
  • the image encoding apparatus may configure a palette table based on the palette predictor.
  • the palette table may include at least one palette entry selected from the palette predictor and a palette index for identifying each palette entry.
  • the palette predictor and the palette table may be variously configured according to the color format (or chroma format) of the current block.
  • the palette predictor and the palette table may include only the palette entry for the luma component of the current block.
  • the palette predictor and the palette table are the luma component of the current block and It may contain a palette entry for each chroma component.
  • the palette predictor and the palette table may be variously configured according to the partition structure of the current block. For example, when the current block has a single tree structure, the palette predictor and the palette table may have one configuration commonly applied to the luma component and the chroma component of the current block. In contrast, when the current block has a dual tree structure, the palette predictor and the palette table may have a plurality of configurations individually applied to each of the luma component and the chroma component of the current block.
  • the palette predictor for the current block may include a luma palette predictor for a luma component and a chroma palette predictor for a chroma component. In this case, the number of palette entries included in the luma palette predictor may be different from the number of palette entries included in the chroma palette predictor.
  • the image encoding apparatus may generate a palette index map for the current block based on the palette table (S2320).
  • the palette index map may mean mapping a predetermined palette index in the palette table to each sample in the current block. For example, among a plurality of samples in the current block, a palette index indicating a corresponding representative color value may be mapped to a sample having the same or similar pixel value as the representative color value defined in the palette table. Alternatively, among a plurality of samples of the current block, an escape palette index may be mapped to a sample (escape sample) having a pixel value that is similar to the representative color value defined in the palette table. In an example, whether a pixel value of each sample is similar to a representative color value defined in the palette table may be determined based on a predetermined threshold.
  • a palette index indicating the representative color value may be mapped to the corresponding sample.
  • an escape palette index may be mapped to the corresponding sample.
  • the image encoding apparatus may encode the current block based on the palette index map (S2330).
  • the encoding process of the current block may be performed by scanning the palette indices in the palette index map according to a predetermined scan method.
  • the apparatus for encoding an image may determine an encoding mode (pallet sample mode) of each of the palette indexes by scanning the palette indexes mapped to the current block according to a predetermined scan method.
  • the scanning method for palette encoding may include a horizontal traverse scan and a vertical traverse scan.
  • information about the scan method may be signaled using palette_transpose_flag.
  • a palette_transpose_flag having a first value (e.g. 0) may be signaled.
  • a palette_transpose_flag having a second value e.g. 1
  • An encoding mode for encoding each of the palette indexes mapped to the current block may be referred to as a palette sample mode.
  • the palette sample mode may include a'INDEX' mode and a'COPY_ABOVE' mode.
  • a value of a corresponding palette index may be encoded.
  • the palette sample mode is set to'COPY_ABOVE' mode, the value of the palette index is not encoded, and the palette index exists in the top (for horizontal traverse scan) or left (for vertical traverse scan).
  • Information indicating that the index has the same value may be encoded.
  • information on the palette sample mode may be signaled using copy_above_palette_indices_flag.
  • a copy_above_palette_indices_flag having a first value e.g. 0
  • a copy_above_palette_indices_flag having a second value e.g. 1
  • run-value information indicating the number of consecutively encoded palette indices using the same palette sample mode may be additionally encoded.
  • a quantized pixel value of the escape sample may be encoded.
  • whether the current block includes an escape sample may be signaled using an escape sample flag (e.g. palette_escape_val_present_flag).
  • an escape sample flag e.g. palette_escape_val_present_flag
  • a palette_escape_val_present_flag having a first value e.g. 0
  • a palette_escape_val_present_flag having a second value e.g. 1
  • the image encoding apparatus may determine whether the split structure of the current block is a local dual tree structure (S2340).
  • whether the partition structure of the current block is a local dual tree structure may be determined based on the prediction mode type of the current block. For example, as described above with reference to FIGS. 10A to 10C, when the prediction mode type of the current block is MODE_TYPE_INTRA to which only intra prediction can be applied, the partition structure of the current block may be a local dual tree structure. In contrast, when the prediction mode type of the current block is not MODE_TYPE_INTRA (e.g. MODE_TYPE_ALL), the split structure of the current block may be a single tree structure.
  • whether the current block partition structure is a local dual tree structure may be determined based on at least one of a tree type of the current block and a partition structure of the current CTU. For example, when the tree type of the current block is not a single tree (SINGLE_TREE), and the current CTU is included in a P or B slice or is divided into a single tree structure, the partition structure of the current block may be a local dual tree structure. . In contrast, when the tree type of the current block is a single tree (SINGLE_TREE), the split structure of the current block may be a single tree structure.
  • the current block is included in the I slice, and the CTU included in the slice is implicit quadtree split into a 64x64 luma sample CU, and the 64x64 luma sample CU includes a root node of a dual tree. If so, the divided structure of the current block may be a dual tree structure. Whether the partition structure of the current block is a local dual tree structure may be signaled using LocalDualTreeFlag as shown in Equation 6 below.
  • sps_qtbtt_dual_tree_intra_flag may represent a split structure of a current CTU.
  • sps_qtbtt_dual_tree_intra_flag having a first value may indicate that the current block is included in the I slice, and the CTU included in the corresponding slice is divided into a single tree structure.
  • sps_qtbtt_dual_tree_intra_flag having a second value includes the current block in the I slice, and the CTU included in the slice is implicit quadtree split into a 64x64 luma sample CU, and the 64x64 luma sample It may be indicated that the CU becomes the root node of the dual tree.
  • the value of LocalDualTreeFlag may be determined based on a tree type of the current block (treeType), a slice type (sh_slice_type), and a split structure (sps_qtbtt_dual_tree_intra_flag) of the current CTU.
  • the first value (eg 0) of LocalDualTreeFlag may indicate that the partition structure of the current block is not a local dual tree structure
  • the second value of LocalDualTreeFlag (eg 1) may indicate that the partition structure of the current block is a local dual tree structure. have.
  • the image encoding apparatus may update the palette predictor using the palette table for the current block (S2350). For example, when the current block is a luma block in a monochrome format, the image encoding apparatus may update the palette predictor. Also, when the current block is a chroma block and the split structure of the current block is not a local dual tree structure, the image encoding apparatus may update the palette predictor. In contrast, when the current block is a chroma block and the split structure of the current block is a local dual tree structure, the image encoding apparatus may not update the palette predictor.
  • the apparatus for encoding an image may update the palette predictor by adding at least one palette entry included in the palette table to the palette predictor.
  • the image encoding apparatus may update the palette predictor by replacing at least one palette entry included in the palette predictor with at least one palette entry included in the palette table.
  • the palette entry replaced in the palette predictor may be determined as the oldest palette entry or the palette entry used with the least frequency according to a first-in-first-out method (FIFO).
  • FIFO first-in-first-out method
  • the process of updating the palette predictor may be continuously performed until the palette predictor reaches a maximum size.
  • the palette predictor does not reach the maximum size, at least one palette entry in the palette predictor that is not reused in the palette table may be added as a new palette predictor. This may be referred to as pallet stuffing.
  • information on the updated palette predictor may be encoded and signaled.
  • the image encoding apparatus may skip updating the palette predictor (S2350).
  • a palette predictor applied to the current block may be applied again to a block that is palette-coded after the current block in the current CTU.
  • step S2340 the step of determining whether the split structure of the current block is a local dual tree structure (S2340) is performed after the step of encoding the current block (S2330), but the order of operations thereof is variously changed. Can be.
  • step S2340 may be performed before step S2330, or step S2340 may be performed simultaneously with step S2330.
  • FIG. 24 is a diagram for describing a palette encoding process when a palette predictor is not updated in the example of FIG. 19.
  • palette entries for the luma component are applied to the palette encoding of the 3-1 luma block 1913-1. It can be used (S2420).
  • palette entries for the chroma component may be used for palette encoding of the third chroma block 1923 (S2430).
  • a process of updating the palette predictor may be skipped.
  • the palette encoding process for the second luma block 1912 may be applied again (S2440).
  • 25 is a diagram illustrating an example of a process of selectively updating a palette predictor based on a partition structure of a current block.
  • a first mode type eg MODE_TYPE_ALL
  • the parameter CurrentPaletteSize[startComp] may represent the size of the palette table for the current block (ie, the total number of palette entries).
  • Each value of the parameters startComp, numComps, and maxNumPalettePredictorSize may be set differently according to the partition tree structure of the current block.
  • values of the parameters startComp, numComps, and maxNumPalettePredictorSize may be set as shown in Equation 7 below.
  • the first color component startComp of the palette table may be set to 0.
  • the total number of color components in the palette table numComps is set to 1 when the color format (or chroma format) of the current block is monochrome, and when the color format of the current block is 4:4:4 Can be set to 3.
  • the maximum size of the palette predictor maxNumPalettePredictorSize may be set to 63.
  • values of the parameters startComp, numComps, and maxNumPalettePredictorSize may be set as shown in Equation 8 below.
  • the first color component startComp of the palette table may be set to 0.
  • the total number of color components in the palette table numComps may be set to 1.
  • the maximum size of the palette predictor maxNumPalettePredictorSize may be set to 31.
  • values of the parameters startComp, numComps, and maxNumPalettePredictorSize may be set as shown in Equation 9 below.
  • the first color component startComp of the palette table may be set to 1. Also, the total number of color components in the palette table numComps may be set to 2. In addition, the maximum size of the palette predictor maxNumPalettePredictorSize may be set to 31.
  • cIdx may mean a color component.
  • 26 is a flowchart illustrating a method of decoding a palette according to an embodiment of the present disclosure.
  • the palette decoding method of FIG. 26 may be performed by the image decoding apparatus of FIG. 3. Specifically, steps S2610 to S2660 may be performed by the intra prediction unit 265 or by a separate functional block (e.g. a palette decoding unit) different from the intra prediction unit 265.
  • steps S2610 to S2660 may be performed by the intra prediction unit 265 or by a separate functional block (e.g. a palette decoding unit) different from the intra prediction unit 265.
  • the image decoding apparatus may obtain palette information and palette index prediction information for a current block from a bitstream (S2610).
  • the palette information may include information on a palette predictor.
  • the palette information may further include information on a new palette entry.
  • the apparatus for decoding an image may obtain information on a palette predictor by decoding PredictorPaletteEntries[cIdx][i] included in a bitstream.
  • the image decoding apparatus may obtain information on a new palette entry by decoding new_palette_entries[cIdx][i] included in the bitstream.
  • cIdx may mean a color component.
  • the palette index prediction information may include information on a palette index map for the current block.
  • the image decoding apparatus may obtain at least one palette index mapped to the current block by decoding PaletteIndexMap[xC][yC] included in the bitstream.
  • xC and yC may be coordinate indicators indicating the relative positions of the current sample from the upper left sample of the CTU (or slice) to which the current block belongs.
  • the image decoding apparatus may obtain run-value information of a palette index included in the palette index map by decoding PaletteRunMinus1 included in the bitstream.
  • the image decoding apparatus may configure a palette predictor and a palette table for the current block based on the palette information obtained from the bitstream (S2620).
  • the image decoding apparatus may configure a palette predictor for the current block based on PredictorPaletteEntries[cIdx][i] included in the bitstream.
  • the palette predictor may have a predetermined value (e.g. 0) initialized at the initial decoding time of the CTU (or slice) including the current block, for example.
  • the palette predictor may have the same configuration as the palette predictor updated in the previous palette decoding process.
  • the image decoding apparatus may configure a palette table for the current block based on the palette predictor.
  • the palette table may include at least one of a palette entry included in the palette predictor and a new palette entry obtained from a bitstream, and a palette index for identifying each palette entry.
  • the palette predictor and the palette table may be variously configured according to the color format (or chroma format) of the current block.
  • the palette predictor and the palette table may include only a palette entry for a luma component or all palette entries for each of the luma component and the chroma component according to the color format of the current block.
  • the palette predictor and the palette table may be variously configured according to the partition structure of the current block. For example, when the current block has a single tree structure, the palette predictor and the palette table may have a single configuration commonly applied to the luma component and the chroma component of the current block. In contrast, when the current block has a dual tree structure, the palette predictor and the palette table may have multiple configurations separately applied to each of the luma component and the chroma component of the current block.
  • the image decoding apparatus may generate a palette index map for the current block based on the palette index prediction information obtained from the bitstream (S2630). Specifically, the image decoding apparatus maps the palette index to each sample in the current block according to a predetermined scan method using the palette index obtained from the bitstream, the palette sample mode, and the run-value of the palette sample mode, You can create a palette index map.
  • the scanning method for pallet decoding may include a horizontal traverse scan and a vertical traverse scan.
  • the scan method for palette decoding may be determined by decoding the palette_transpose_flag included in the bitstream. For example, when palette_transpose_flag has a first value (e.g. 0), a scan method for palette decoding may be determined as a horizontal traverse scan. In contrast, when palette_transpose_flag has a second value (e.g. 1), a scan method for palette decoding may be determined as a vertical traverse scan.
  • the palette sample mode may include a'INDEX' mode and a'COPY_ABOVE' mode.
  • the value of the palette index mapped to the current sample may be obtained directly from the bitstream.
  • the value of the palette index mapped to the current sample is present above the current sample (in the case of a horizontal traverse scan) or left (in the case of a vertical traverse scan). It may be determined as a value of the palette index mapped to the surrounding samples.
  • the quantized pixel value of the current sample may be obtained directly from the bitstream.
  • An escape palette index may be mapped to the escape sample.
  • the image decoding apparatus may decode the current block based on the palette table and the palette index map for the current block (S2640). Specifically, the image decoding apparatus may generate a prediction block for the current block by inverse mapping a value of each palette index in the palette index map to a representative color value by referring to the palette table.
  • the image decoding apparatus may determine whether the current block has a local dual tree structure (S2650).
  • whether the partition structure of the current block is a local dual tree structure may be determined based on the prediction mode type of the current block. For example, as described above with reference to FIGS. 10A to 10C, when the prediction mode type of the current block is MODE_TYPE_INTRA to which only intra prediction can be applied, the partition structure of the current block may be a local dual tree structure. In contrast, when the prediction mode type of the current block is not MODE_TYPE_INTRA (e.g. MODE_TYPE_ALL), the split structure of the current block may be a single tree structure.
  • whether the split structure of the current block is a local dual tree structure may be determined based on at least one of a tree type of the current block and a split structure of a CTU (current CTU) including the current block. For example, when the tree type of the current block is not a single tree (SINGLE_TREE) and the current CTU is divided into a single tree structure, the partition structure of the current block may be a local dual tree structure. In contrast, when the tree type of the current block is a single tree (SINGLE_TREE), the split structure of the current block may be a single tree structure.
  • the current block is included in the I slice, and the CTU included in the slice is implicit quadtree split into a 64x64 luma sample CU, and the 64x64 luma sample CU includes a root node of a dual tree.
  • the divided structure of the current block may be a dual tree structure.
  • Whether the partition structure of the current block is a local dual tree structure may be determined by decoding the above-described LocalDualTreeFlag with reference to Equation 6. For example, when LocalDualTreeFlag has a first value (e.g. 0), the partition structure of the current block may be determined as a single tree structure or a dual tree structure. In contrast, when LocalDualTreeFlag has a second value (e.g. 1), the partition structure of the current block may be determined as a local dual tree structure.
  • the image decoding apparatus may update the palette predictor using the palette table for the current block (S2660). For example, when the current block is a luma block in a monochrome format, the video decoding apparatus may update the palette predictor. In addition, when the current block is a chroma block and the split structure of the current block is not a local dual tree structure, the image decoding apparatus may update the palette predictor. In contrast, when the current block is a chroma block and the split structure of the current block is a local dual tree structure, the image decoding apparatus may not update the palette predictor.
  • the image decoding apparatus may update the palette predictor by adding at least one palette entry included in the palette table to the palette predictor.
  • the image decoding apparatus may update the palette predictor by replacing at least one palette entry included in the palette predictor with at least one palette entry included in the palette table.
  • the palette entry replaced in the palette predictor may be determined as the oldest palette entry or the palette entry used with the least frequency according to a first-in-first-out method (FIFO).
  • the process of updating the palette predictor may be continuously performed until the palette predictor reaches a maximum size.
  • the palette predictor does not reach the maximum size, at least one palette entry in the palette predictor that is not reused in the palette table may be added as a new palette predictor. This may be referred to as pallet stuffing.
  • the image decoding apparatus may update the palette predictor based on update information of the palette predictor signaled from the image encoding apparatus.
  • the video decoding apparatus may skip updating the palette predictor (S2660).
  • a palette predictor applied to the current block may be reapplied to a block whose palette is decoded after the current block in the current CTU.
  • Embodiment #1 of the present disclosure described above when the partition structure of the current block is a local dual tree structure, a process of updating a palette predictor applied to the current block may be skipped. Accordingly, a problem in which the palette predictor for a block that is palette-encoded/decoded next to the current block does not include a valid palette entry applied to the current block or includes an invalid palette entry is solved. I can.
  • the palette mode in encoding/decoding a current block having a local dual tree structure, the palette mode may be selectively applied based on the split structure of the current block.
  • FIG. 27 is a flowchart illustrating a palette encoding method according to an embodiment of the present disclosure.
  • the palette encoding method of FIG. 27 may be performed by the image encoding apparatus of FIG. 2. Specifically, S2710 to S2760 may be performed by the intra prediction unit 165 or by a separate functional block (e.g. palette encoding unit) different from the intra prediction unit 165. Meanwhile, S2720 to S2750 of FIG. 27 may correspond to S2310 to S2330 and S2350 of FIG. 23, respectively. Therefore, the description of S2720 to S2750 will be briefly described.
  • the apparatus for encoding an image may determine whether a split structure of a current block is a local dual tree structure (S2710).
  • whether the partition structure of the current block is a local dual tree structure may be determined based on the prediction mode type of the current block. For example, as described above with reference to FIGS. 10A to 10C, when the prediction mode type of the current block is MODE_TYPE_INTRA to which only intra prediction can be applied, the partition structure of the current block may be a local dual tree structure. In contrast, when the prediction mode type of the current block is not MODE_TYPE_INTRA (e.g. MODE_TYPE_ALL), the split structure of the current block may be a single tree structure.
  • whether the current block partition structure is a local dual tree structure may be determined based on at least one of a tree type of the current block and a partition structure of the current CTU. For example, when the tree type of the current block is not a single tree (SINGLE_TREE), and the current CTU is included in a P or B slice or is divided into a single tree structure, the partition structure of the current block may be a local dual tree structure. . In contrast, when the tree type of the current block is a single tree (SINGLE_TREE), the split structure of the current block may be a single tree structure.
  • the current block is included in the I slice, and the CTU included in the slice is implicit quadtree split into a 64x64 luma sample CU, and the 64x64 luma sample CU includes a root node of a dual tree. If so, the divided structure of the current block may be a dual tree structure. Whether the split structure of the current block is a local dual tree structure may be signaled using LocalDualTreeFlag described above with reference to Equation 6.
  • the first value (eg 0) of LocalDualTreeFlag may indicate that the partition structure of the current block is not a local dual tree structure
  • the second value (eg 1) of LocalDualTreeFlag is the partition structure of the current block is a local dual tree structure. Can indicate that it is.
  • the video encoding apparatus determines to apply the palette mode to the current block, and constructs a palette predictor and palette table for the current block. It can be done (S2720).
  • the palette predictor may include at least one palette entry (representative color value) and a palette index for identifying each palette entry.
  • the palette predictor may have a predetermined initial value (e.g. 0).
  • the palette predictor may include at least one palette entry used in a palette encoding process prior to the current block in the current CTU.
  • the image encoding apparatus may configure a palette table based on the palette predictor.
  • the palette table may include at least one palette entry selected from the palette predictor and a palette index for identifying each palette entry.
  • the palette predictor and the palette table may be variously configured according to the color format (or chroma format) of the current block.
  • the palette predictor and the palette table may include only the palette entry for the luma component of the current block.
  • the palette predictor and the palette table are the luma component of the current block and It may contain a palette entry for each chroma component.
  • the palette predictor and the palette table may be variously configured according to the partition structure of the current block. For example, when the current block has a single tree structure, the palette predictor and the palette table may have one configuration commonly applied to the luma component and the chroma component of the current block. In contrast, when the current block has a dual tree structure, the palette predictor and the palette table may have a plurality of configurations individually applied to each of the luma component and the chroma component of the current block.
  • the image encoding apparatus may generate a palette index map for the current block based on the palette table (S2730). Specifically, the image encoding apparatus maps a palette index to each pixel in the current block, based on whether the pixel value of each pixel (sample) in the current block is the same or similar between the pixel value of each pixel (sample) in the current block and the representative color value in the palette table. You can create a map.
  • the image encoding apparatus may encode the current block based on the palette index map (S2740).
  • the encoding process of the current block may be performed by scanning the palette indices in the palette index map according to a predetermined scan method.
  • the apparatus for encoding an image may determine an encoding mode (pallet sample mode) of each of the palette indexes by scanning the palette indexes mapped to the current block according to a predetermined scan method.
  • the scanning method for palette encoding may include a horizontal traverse scan and a vertical traverse scan.
  • information about the scan method may be signaled using palette_transpose_flag.
  • the palette sample mode for encoding each of the palette indexes included in the palette index map may include a'INDEX' mode and a'COPY_ABOVE' mode.
  • a value of a corresponding palette index may be encoded.
  • the palette sample mode is set to'COPY_ABOVE' mode, the value of the palette index is not encoded, and the palette index exists in the top (for horizontal traverse scan) or left (for vertical traverse scan).
  • Information indicating that the index has the same value may be encoded.
  • information on the palette sample mode may be signaled using copy_above_palette_indices_flag.
  • run-value information indicating the number of consecutively encoded palette indices using the same palette sample mode may be additionally encoded.
  • information indicating whether the palette index map includes an escape palette index may be signaled using an escape sample flag (e.g. palette_escape_val_present_flag).
  • an escape sample flag e.g. palette_escape_val_present_flag.
  • a quantized pixel value of the sample may be encoded and signaled.
  • the image encoding apparatus may update the palette predictor by using the palette table for the current block (S2750). For example, the image encoding apparatus may update the palette predictor by adding at least one palette entry included in the palette table to the palette predictor. In addition, the image encoding apparatus may update the palette predictor by replacing at least one palette entry included in the palette predictor with at least one palette entry included in the palette table. The palette entry replaced in the palette predictor may be determined as the oldest palette entry or the least frequently used palette entry according to a first-in-first-out method (FIFO).
  • FIFO first-in-first-out method
  • the process of updating the palette predictor may be continuously performed until the palette predictor reaches the maximum palette size.
  • the pallet predictor can be updated through pallet stuffing until a maximum pallet size is reached.
  • the video encoding apparatus does not apply the palette mode to the current block, and normal prediction modes other than the palette mode (eg intra prediction mode, inter prediction mode). Mode, etc.) may be used to encode the current block (S2760). Details of the conventional prediction mode are as described above with reference to FIGS. 1 to 14.
  • palette mode flag e.g. pred_mode_plt_flag
  • FIG. 28 is a diagram illustrating a specific example of a coding_unit syntax including a palette mode flag.
  • pred_mode_plt_flag may indicate whether a palette mode is applied to a current block (or a current CU). For example, pred_mode_plt_flag having a first value (e.g. 0) may indicate that the palette mode is not applied to the current block. Unlike this, pred_mode_plt_flag having the second value (e.g. 1) may indicate that the palette mode is applied to the current block.
  • pred_mode_plt_flag may be signaled based on the prediction mode type of the current block. For example, when the prediction mode type of the current block is a first mode type (e.g. MODE_TYPE_ALL) to which all of intra prediction, intra block copy (IBC), palette mode, and inter prediction can be applied, pred_mode_plt_flag may be signaled. In contrast, when the prediction mode type of the current block is a second mode type to which only intra prediction can be applied (eg MODE_TYPE_INTRA) or a third mode type to which only inter prediction can be applied (eg MODE_TYPE_INTER), pred_mode_plt_flag may not be signaled. have.
  • a first mode type e.g. MODE_TYPE_ALL
  • 29 is a flowchart illustrating a method of decoding a palette according to an embodiment of the present disclosure.
  • the palette decoding method of FIG. 29 may be performed by the image decoding apparatus of FIG. 3. Specifically, steps S2910 to S2980 may be performed by the intra prediction unit 265 or by a separate functional block (e.g. a palette decoding unit) different from the intra prediction unit 265. Meanwhile, S2930 to S2970 of FIG. 29 may correspond to S2610 to S2640 and S2660 of FIG. 26, respectively. Therefore, the description of S2930 to S2970 will be briefly described.
  • the apparatus for decoding an image may determine whether a split structure of a current block is a local dual tree structure (S2910).
  • whether the partition structure of the current block is a local dual tree structure may be determined based on the prediction mode type of the current block. For example, as described above with reference to FIGS. 10A to 10C, when the prediction mode type of the current block is MODE_TYPE_INTRA to which only intra prediction can be applied, the partition structure of the current block may be a local dual tree structure. In contrast, when the prediction mode type of the current block is not MODE_TYPE_INTRA (e.g. MODE_TYPE_ALL), the split structure of the current block may be a single tree structure.
  • whether the current block partition structure is a local dual tree structure may be determined based on at least one of a tree type of the current block and a partition structure of the current CTU. For example, when the tree type of the current block is not a single tree (SINGLE_TREE), and the current CTU is included in a P or B slice or is divided into a single tree structure, the partition structure of the current block may be a local dual tree structure. . In contrast, when the tree type of the current block is a single tree (SINGLE_TREE), the split structure of the current block may be a single tree structure.
  • the current block is included in the I slice, and the CTU included in the slice is implicit quadtree split into a 64x64 luma sample CU, and the 64x64 luma sample CU includes a root node of a dual tree. If so, the divided structure of the current block may be a dual tree structure. Whether the split structure of the current block is a local dual tree structure may be signaled using LocalDualTreeFlag described above with reference to Equation 6.
  • the first value (eg 0) of LocalDualTreeFlag may indicate that the partition structure of the current block is not a local dual tree structure
  • the second value (eg 1) of LocalDualTreeFlag is the partition structure of the current block is a local dual tree structure. Can indicate that it is.
  • the image decoding apparatus may determine whether the palette mode is applied to the current block. In an example, the image decoding apparatus may determine whether the palette mode is applied to the current block based on the palette mode flag (e.g. pred_mode_plt_flag) obtained from the bitstream. For example, when pred_mode_plt_flag described above with reference to FIG. 28 has a first value (e.g. 0), the palette mode may not be applied to the current block. In contrast, when pred_mode_plt_flag has a second value (e.g. 1), the palette mode may be applied to the current block. Meanwhile, when pred_mode_plt_flag is not obtained from the bitstream, it may be inferred that the value of pred_mode_plt_flag has the first value.
  • pred_mode_plt_flag when pred_mode_plt_flag is not obtained from the bitstream, it may be inferred that the value of pred_mode_plt
  • the image decoding apparatus may obtain palette information and palette index prediction information for the current block from the bitstream (S2930).
  • the palette information may include information about a palette predictor and/or a new palette entry.
  • the palette index prediction information may include a palette index mapped to the current block and run-value information of the palette index.
  • the image decoding apparatus may configure a palette predictor and a palette table for the current block based on the palette information obtained from the bitstream (S2940).
  • the palette predictor may have the same configuration as the palette predictor updated in a process of decoding a palette prior to the current block.
  • the palette predictor may have a predetermined initial value (eg 0), or may have the same configuration as the palette predictor used in the previous palette decoding process. .
  • the image decoding apparatus may configure a palette table for the current block based on the palette predictor.
  • the palette table may include at least one of a palette entry included in the palette predictor and a new palette entry obtained from a bitstream, and a palette index for identifying each palette entry.
  • the palette predictor and the palette table may be variously configured according to the color format (or chroma format) of the current block.
  • the palette predictor and the palette table may be variously configured according to the partition structure of the current block.
  • the image decoding apparatus may generate a palette index map for the current block based on the palette index prediction information (S2950). Specifically, the image decoding apparatus maps the palette index to each sample in the current block according to a predetermined scan method using the palette index obtained from the bitstream, the palette sample mode, and the run-value of the palette sample mode, You can create a palette index map.
  • the scanning method for pallet decoding may include a horizontal traverse scan and a vertical traverse scan.
  • the scan method for palette decoding may be determined by decoding the palette_transpose_flag included in the bitstream. For example, when palette_transpose_flag has a first value (e.g. 0), a scan method for palette decoding may be determined as a horizontal traverse scan. In contrast, when palette_transpose_flag has a second value (e.g. 1), a scan method for palette decoding may be determined as a vertical traverse scan.
  • the palette sample mode may include a'INDEX' mode and a'COPY_ABOVE' mode.
  • the value of the palette index mapped to the current sample may be obtained directly from the bitstream.
  • the value of the palette index mapped to the current sample is present above the current sample (in the case of a horizontal traverse scan) or left (in the case of a vertical traverse scan). It may be determined as a value of the palette index mapped to the surrounding samples.
  • the quantized pixel value of the current sample may be obtained directly from the bitstream.
  • An escape palette index may be mapped to the escape sample.
  • the image decoding apparatus may decode the current block based on the palette table and the palette index map for the current block (S2960). Specifically, the image decoding apparatus may generate a prediction block for the current block by inverse mapping a value of each palette index in the palette index map to a representative color value by referring to the palette table.
  • the image decoding apparatus may update the palette predictor by using the palette table for the current block (S2970). For example, the image decoding apparatus may update the palette predictor by adding at least one palette entry included in the palette table to the palette predictor. In addition, the image decoding apparatus may update the palette predictor by replacing at least one palette entry included in the palette predictor with at least one palette entry included in the palette table.
  • the process of updating the palette predictor may be continuously performed until the palette predictor reaches the maximum palette size.
  • the pallet predictor can be updated through pallet stuffing until a maximum pallet size is reached.
  • the image decoding apparatus may update the palette predictor based on update information of the palette predictor signaled from the image encoding apparatus.
  • the video decoding apparatus does not apply the palette mode to the current block, and a normal prediction mode other than the palette mode (eg intra prediction mode, inter prediction mode). Mode, etc.) may be used to decode the current block (S2980). Details of the conventional prediction mode are as described above with reference to FIGS. 1 to 14. In this case, a palette predictor initialized to a predetermined value (e.g. 0) may be applied to a block whose palette is decoded after the current block in the current CTU, or a palette predictor applied to the current block may be applied again.
  • a predetermined value e.g. 0
  • the current block when the split structure of the current block is a local dual tree structure, the current block may be encoded/decoded using a normal prediction mode other than the palette mode. Accordingly, since the process of updating the palette predictor is also skipped, a problem in which the palette predictor does not include a valid palette entry or includes an invalid palette entry can be solved.
  • the exemplary methods of the present disclosure are expressed as a series of operations for clarity of description, this is not intended to limit the order in which steps are performed, and each step may be performed simultaneously or in a different order if necessary.
  • the exemplary steps may include additional steps, other steps may be included excluding some steps, or may include additional other steps excluding some steps.
  • an image encoding apparatus or an image decoding apparatus performing a predetermined operation may perform an operation (step) of confirming an execution condition or situation of a corresponding operation (step). For example, when it is described that a predetermined operation is performed when a predetermined condition is satisfied, the video encoding apparatus or the video decoding apparatus performs an operation to check whether the predetermined condition is satisfied, and then performs the predetermined operation. You can do it.
  • various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof.
  • one or more ASICs Application Specific Integrated Circuits
  • DSPs Digital Signal Processors
  • DSPDs Digital Signal Processing Devices
  • PLDs Programmable Logic Devices
  • FPGAs Field Programmable Gate Arrays
  • general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, or the like.
  • the image decoding device and the image encoding device to which the embodiment of the present disclosure is applied include a multimedia broadcasting transmission/reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, and a real-time communication device such as video communication , Mobile streaming devices, storage media, camcorders, video-on-demand (VoD) service providers, OTT video (Over the top video) devices, Internet streaming service providers, three-dimensional (3D) video devices, video telephony video devices, and medical use. It may be included in a video device or the like, and may be used to process a video signal or a data signal.
  • an OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).
  • FIG. 30 is a diagram illustrating a content streaming system to which an embodiment according to the present disclosure can be applied.
  • the content streaming system to which the embodiment of the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.
  • the encoding server serves to generate a bitstream by compressing content input from multimedia input devices such as a smartphone, a camera, and a camcorder into digital data, and transmits it to the streaming server.
  • multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate bitstreams
  • the encoding server may be omitted.
  • the bitstream may be generated by an image encoding method and/or an image encoding apparatus to which an embodiment of the present disclosure is applied, and the streaming server may temporarily store the bitstream while transmitting or receiving the bitstream.
  • the streaming server may transmit multimedia data to a user device based on a user request through a web server, and the web server may serve as an intermediary for notifying the user of a service.
  • the web server transmits the request to the streaming server, and the streaming server transmits multimedia data to the user.
  • the content streaming system may include a separate control server, and in this case, the control server may play a role of controlling a command/response between devices in the content streaming system.
  • the streaming server may receive content from a media storage and/or encoding server. For example, when content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.
  • Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, and Tablet PC, ultrabook, wearable device, e.g., smartwatch, smart glass, head mounted display (HMD), digital TV, desktop There may be computers, digital signage, etc.
  • PDA personal digital assistant
  • PMP portable multimedia player
  • Tablet PC ultrabook
  • wearable device e.g., smartwatch, smart glass, head mounted display (HMD), digital TV, desktop
  • HMD head mounted display
  • digital TV desktop
  • desktop There may be computers, digital signage, etc.
  • Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be distributedly processed.
  • the scope of the present disclosure is software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause an operation according to the method of various embodiments to be executed on a device or computer, and such software or It includes a non-transitory computer-readable medium (non-transitory computer-readable medium) which stores instructions and the like and is executable on a device or a computer.
  • a non-transitory computer-readable medium non-transitory computer-readable medium
  • An embodiment according to the present disclosure may be used to encode/decode an image.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

L'invention concerne un procédé et un dispositif de codage/décodage d'image. Un procédé de décodage d'image selon la présente divulgation comprend les étapes consistant à : acquérir des informations de palette et des informations de prédiction d'indice de palette concernant le bloc actuel à partir d'un train de bits, lorsqu'un mode palette est appliqué au bloc actuel ; former un prédicteur de palette pour le bloc actuel sur la base des informations de palette, et former une table de palette pour le bloc actuel sur la base du prédicteur de palette ; générer une carte d'indice de palette pour le bloc actuel sur la base des informations de prédiction d'indice de palette ; et décoder le bloc actuel sur la base de la table de palette et de la carte d'indice de palette, le prédicteur de palette pouvant être mis à jour sélectivement sur la base d'une structure de division du bloc actuel.
PCT/KR2020/012898 2019-09-23 2020-09-23 Procédé et dispositif de codage/décodage d'image utilisant un mode palette, et procédé de transmission de train de bits WO2021060844A1 (fr)

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KR1020227008747A KR20220047834A (ko) 2019-09-23 2020-09-23 팔레트 모드를 이용한 영상 부호화/복호화 방법, 장치 및 비트스트림을 전송하는 방법
JP2022518236A JP7362910B2 (ja) 2019-09-23 2020-09-23 パレットモードを用いた画像符号化／復号化方法、装置、及びビットストリームの伝送方法
CN202080066527.8A CN114521328A (zh) 2019-09-23 2020-09-23 使用调色板模式的图像编码/解码方法和装置及发送比特流的方法
CA3155112A CA3155112A1 (fr) 2019-09-23 2020-09-23 Procede et dispositif de codage/decodage d'image utilisant un mode palette, et procede de transmission de train de bits
US17/697,474 US11689732B2 (en) 2019-09-23 2022-03-17 Image encoding/decoding method and device using palette mode, and method for transmitting bitstream
US18/198,170 US12003740B2 (en) 2019-09-23 2023-05-16 Image encoding/decoding method and device using palette mode, and method for transmitting bitstream
JP2023172537A JP2023171923A (ja) 2019-09-23 2023-10-04 パレットモードを用いた画像符号化／復号化方法、装置、及びビットストリームの伝送方法

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US201962904578P 2019-09-23 2019-09-23
US62/904,578 2019-09-23

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US17/697,474 Continuation US11689732B2 (en) 2019-09-23 2022-03-17 Image encoding/decoding method and device using palette mode, and method for transmitting bitstream

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KR20210116676A (ko) * 2019-03-14 2021-09-27 엘지전자 주식회사 인트라 예측을 수행하는 영상 부호화/복호화 방법, 장치 및 비트스트림을 전송하는 방법
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CA3155112A1 (fr) 2021-04-01
KR20220047834A (ko) 2022-04-19
US12003740B2 (en) 2024-06-04
CN114521328A (zh) 2022-05-20
US20230291915A1 (en) 2023-09-14
US11689732B2 (en) 2023-06-27
JP2022549263A (ja) 2022-11-24

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